It's easy, simply open Apps gui, go to the Apps button and select Maintenance > Dependencies and Deletions (allow a minute or two to build the list.
Then select the extension you wish to delete.
Then while the app you wish to delete is selected open the dependencies button > and select "Mark for Deletion"
On next reboot the extension will be deleted, additionally any dependencies which are not required by any other extension will also be deleted.
End of story.
There is however a fail-safe mechanism. In the event you have manually accidentally removed/deleted a needed extension, use the "Fetch missing Dependencies" from the same Dependencies button. Run that to resolve missing deps.