Deleting a candidate move is a performance intensive action if you are deleting complex branches. Instead of deleting any candidate moves it is recommended to copy each sub-system into a new opening and then deleting the original opening as a whole, which is very fast. Let’s assume you’ve imported a PGN file, which contains a complete repertoire. Then just go to the key positions, which define each sub-system. Use the Copy command, create a new opening and then use Add Moves command to add the moves of the sub-system to this newly created opening. Once you have done this for all sub-systems you can delete the original opening, which contained all sub-systems.