If you have an external hard drive, first thing, create an image of your existing drive. Also, if memory serves, although they officially ended free upgrades from windows 7 or 8 to windows 10 a few years back, the last times I’ve tried it in the last few months, it still worked.
Usually you can go and download the windows 10 media creation tool, and tell it to upgrade your pc and keep all your files and apps.
Here’s a guide to a windows 7 image backup, just in case you need it.
https://www.passfab.com/windows-7/create-disk-image-windows-7.html
What you could do, create an image onto an external hard drive, when your ssd arrives, pull out your hard drive and install the ssd, then boot up with the repair disc you created from the article, and restore the windows 7 image onto your ssd.
Once you do that, you should be able to boot up from the ssd and it look just like your windows 7 install. Then run the windows 10 media creation tool, tell it to upgrade this pc, and keep all your files and apps.
If all goes well, after the upgrade, you should have the ssd running with windows 10 installed and activated, and all of your programs and files as they were in windows 7.
Also if you unplugged the other drive after creating the image, then you’ll have it to pull files from.
You could also unplug your hard drive and do a clean install of windows 10 on your ssd, then plug your old drive in later. Personally though the clone method is handy if you don’t want to tinker much.