Hey there 
I recommend having a look over in your data files from The Forge
Particularly in the Other tab. We’ve often seen that after an install of a premium module, a .zip file doesn’t get cleaned up by Foundry which can result in up to a few hundreds of MB being used.
If any of your modules themselves are in the tens of MB, it’s possible that they did not optimize assets properly to your Assets Library during install. I’d recommend simply deleting and re-installing those one at a time to let the optimization step retry.
That should give you plenty of space again, though if you run into any trouble, please feel free to post a screenshot showing what modules or files are using up all of that space!
Additional storage can be purchased from The Forge but I’d first advise you check your game data in Select Data Files to Delete, since it’s possible you won’t need it!
