(Tablet / Smartphone) Is there a way to delete files I don't need?

Select Delete backup files in the Reset to original defaults dialog.

Delete backup files can reduce the size of the app.

Note:
From September 26 2023, Clip Studio Paint Ver. 2.2.0 features a Delete backup files feature.
See here to update to the latest version.

Steps

2. In the Reset to original defaults dialog, check OK for Delete backup files.

Note:
Check only the items you wish to restore to their defaults.
Make sure to check just Delete backup files.

3. Tap OK in the confirmation dialog and the backup files will be deleted.