Downloaded but unused designs/themes cost a lot of disk space, so it is advisable to remove unused designs from your LG device.

Android 9 | LG UX 9.0
Step 1:  Open the  Settings
Step 2:  Tap on  Display
Step 3:  Tap on  Wallpaper & theme
Step 4:  Tap on  Theme
Step 5:  Tap on desired  Theme
Step 6:  Tap on  Remove
Step 7:  Confirm with  Delete
  1. Open the Settings
  2. Tap on Display
  3. Tap on Wallpaper & theme
  4. Tap on Theme
  5. Tap on desired Theme
  6. Tap on Remove
  7. Confirm with Delete

LG Instructions