Then why are you asking how to increase the tempo? Mix without sync, enabling you to adjust the BPM. Or if you must use sync, engage it only when you need to. Turn it off, adjust tempo, turn it back on.
Yup, PK has it right. If I ever use sync, I disengage sync on the track that I’m going to bring in and move the fader to the BPM of the playing track, then reengage sync, after I’ve fully mixed that track in, I can adjust the BPM slowly up or down to my desired BPM without that “jump” effect. Rinse and repeat.
I would search the request section and if there is no request for this, I think it would be a good idea to have an option to unlock this on the master deck if the user wanted to. Not sure how the layers would like that but I guess the soft takeover might cover that.
I know it is frowned upon to change the master bpm but there are exceptions where you can do it and still have it sound good, or not noticed. Perhaps a bit harder to hide with EDM.
I don’t do this very often but it would save you from having to turn off sync each time and FWIW I think Traktor lets you do this too (not certain).
It could be like is in the competitors decks - Master deck can change tempo via Pitch fader, and all synced devices should follow the master tempo.
So the pitch fader should be unlocked on Master deck/layer, all synced devices should act as slave to bpm/grid of the master.