Some designs/themes from the Samsung Galaxy Store only require a few MB, while others do not. If you want to clean up the memory of your Samsung device, you have the option of deleting unused designs. Both purchased and free themes can then be downloaded again and again.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Themes
Step 3:  Open the  menu
Step 4:  Tap on  My Stuff
Step 5:  Tap on desired  Theme
Step 6:  Tap on  Delete
Step 7:  Confirm with  Delete
  1. Open the Settings
  2. Tap on Themes
  3. Open the menu
  4. Tap on My Stuff
  5. Tap on desired Theme
  6. Tap on Delete
  7. Confirm with Delete

Samsung Instructions