so, I've been wondering how to change where save data is saved, My C drive is full which is where it tries to save even though the game is on the D drive. Because of this, I cant save my progress can anyone help please?

What you should do, is clean out your C: drive. If it is that full, then you're basically killing the drive - it will stop working much sooner than a well-maintained drive.

Almost all games save their savegames to the Appdata folder, or (if they are older) to the Documents folder. It doesn't matter where you install the games. Savegames belong into the User area, and the User area is (by default) on the C: drive.

Theoretically you can move these folders, but it is complicated and error-prone (you have to create symlinks, and some games may have locations on the C: drive hardcoded and will break). I wouldn't recommend it unless you're 100% sure of what you're doing. Instead, look for other things on that drive that you can move. Buying a larger drive would of course also work.

Thanks for you’re help, but the reason that I don’t clean out the drive is because it has just My OS, that’s pretty much it, so If I do get a new SSD how would I move everything to it?

You can use Steam to move the game to another drive. You can move several of them over to a secondary drive to make room. Can't remember if the save file folders get moved too or not, but the actual game files, definitely. That should free up space for you.

I've done this dozens of times without issue. Don't ever attempt to move a Steam game manually using Windows file manager! There are hidden files and stuff involved and all you will end up doing is screwing up your game library! Let Steam do it!