Start with cleaning up the desktop.
Let me give you a slight head start on the migration.
Using XMP
When you edit in Lightroom (a raw file) the edits are stored in the catalog, but you can also write them separately to a "sidecar" file. For Nikon this means you have a FILENAME.NEF as the raw file, and beside it as FILENAME.XMP. by default this does not occur, but you can do it with the menu options METADATA, SAVE METADATA TO FILES with all the files selected first. You can also set a preference so it is done automatically: Edit, Catalog Settings, Metadata, Automatically write changes to XMP, which you could set on the laptop to always have them ready.
Stored in the XMP are all the develop settings, and most metadata. Absent are cross-image items like presence in collections, stacking, etc.
If you take just those two files and make them available on your desktop, then do an import, PROVIDED you do not also overwrite the settings with any develop presets applied during import, then they come in with all the develop settings and metadata present already. You can make them available most easily, if you are a bit windows literate, by sharing your laptop drive to the desktop, and importing directly from where they were saved on the laptop (do an import/copy not import/add or import/move). In this way there's really no preparation, you can do it as soon as you get home and plug in (just leave the share present). Once safely confirmed to be on the desktop, you can delete from the laptop using Lightroom (delete from disk option).
In doing this you need to be aware of things that might be done twice, e.g. I mentioned develop presets applied on the laptop should not be applied during import, but also file renaming, metadata presets, etc. should generally not be done again as they overwrite what was on the laptop.
Using Catalog
I rarely do this so am not going to give you a play by play, but fundamentally you need to get some or all of your laptop catalog visible from your desktop, including the images, AND have the image paths be correct. You can copy the catalog and images over, you can export a portion of the catalog to a new catalog and copy that (and images). The trick is that on the desktop the new catalog has to be functional, meaning that the path that lead to the images on the laptop (e.g. c:\myphotos\20171201\image.mef) has to end up being the same on the desktop, and/or you have to fix it. Once the new catalog is functional (you can actually open it and check), then you open your desktop catalog and import the transfer one. Getting the paths right is the most difficult part for most people who do not live and breath computers.
The catalog import is a bit more complete, and also does a merge, so if you try bringing in the same image more than once it will flag that (the XMP process will also to a lesser degree). It also doesn't try applying presets of any type, so you do not need to worry about that.
Personally I've done both, but do the vast majority of my moves with XMP data as it is simple and fast. Others I know vastly prefer catalog merges. Both are reasonably well documented and fully supported by Adobe (as opposed to trying to sync catalogs; not meaning to imply adobe will support you with help, just that they won't claim it broke Lightroom).
Caveats to both
Both assume you have identical setups in some areas that are not automatic. Your preferences should generally be similar, especially ones that affect file handling (e.g. treat jpg with raw as separate), metadata characters and other how-to-apply-metadata settings. You also need to have identical camera and lens profiles on both if you have created any yourself (lightroom will keep its own the same if you run the same lightroom version on both, it is your own that you need to worry about). You also need to take care with third party plugins that might be auto-action-related, e.g. publishing (you don't want to sync to the same web site from both, generally, at least not without knowing exactly what you are doing). Perhaps the biggest issue is to find a path (pun intended) for transfer of data that YOU completely and totally understand, and do it the same way each time, so that you do not have files go missing in movement, or double up and discover them months later wondering "how did this get there". So that means once fully migrated in one direction and backed up there, delete the old, entirely.
And remember this works best as a one way migration. You can migrate an image back, but the issues come in then when you try to take it back the other way, especially if both have been edited separately.