Read this: Windows 10 Upgrade on Dell Latitude D610
Take a look on my reply, full instructions provided.
Basically speaking, Dell only officially supports Windows 2000 and Windows XP on Dell Latitude D610 (and other Dx10 models).
However it can definitely run Windows Vista and 7 at the very least, as long as you max out the RAM (2GB, 2 x 1GB, can be bought cheaply in eBay) and manually install the drivers, particularly the graphics driver, look at Device Manager and see what drivers are needed.
If you're lucky to have a D610 with ATi graphics then you can even run Windows 8 and 10 with all drivers available, and I can tell you it won't be dog slow contrary to many people say, as I do have something similar (an HP Compaq nx8220) in frequent use. Keep the system as lean as possible (i.e. no bloatwares, anti-virus etc.) and it'll serve you well.