Samsung
Remove a Theme auf Samsung
Themes downloaded from the Galaxy Store stay stored on your device even after you switch to a different look. Purchased and free designs behave the same way here: once installed, they sit in local storage until you remove them manually.
The Themes area lives inside the Settings app on Samsung devices and manages every design you have downloaded, including the ones you are not currently using. Deleting a theme only removes the local files, not your purchase record, so a paid design can be downloaded again later at no extra cost.
To delete a theme, go to Tap on Settings ➔ Tap on Themes ➔ Open the Menu ➔ Tap on My stuff ➔ Choose a Theme ➔ Tap on Delete ➔ Tap on Delete to confirm.
This only removes the theme files, not the theme you have currently applied to your home screen and lock screen. If you delete the active theme, your device switches back to the default look automatically.
If storage is tight across the whole device rather than just from themes, check installed apps and cached data as well, since themes are rarely the biggest storage consumer on their own.