Welcome to the forum Rose100xy!
I believe you are really talking about your disk storage space, not RAM. The Transformer T100 comes with 64GB of disk storage and with the OS and other software on there from the factory probably leaves you with less than half that for your own use.
I don't have any experience with the T100 but have a Surface Pro 3 tablet. My Surface has 128GB of storage so better off than you, but it still needs to be managed.
One of the things you can do is to get a 64GB or 128GB microSD card to use as secondary storage (Personally, I have a 128GB card as secondary storage on my Surface) and use it for your data storage and save the internal storage for the OS and programs you install. You can also install programs to the microSD card but they will run slower there.
As far as you losing disk space, from Windows Explorer, right-click on the C: drive and select Properties. Near the bottom right of the Properties dialog is a button labeled "Disk Cleanup". Click on it and let it run to see if it can recover disk space for you by identifying files that can safely be deleted and then delete them with your OK. This should help you reclaim some of your lost disk space.