sell back all abilities?

ok peeps, some of the abilities i have bought arent that great (turrets etc). i thought you could sell individual ones but i cant see where, just sell all.

with sell all it says you lose a rank. so im rank 16 now, i would go to 15 and still be able to get to 20? its a bit confusing. i dont mind redoing 1 rank as its only 3 games or so to do that. i just dont want to miss out in the end, i still want to have 20 abilities at my disposal by rank 20

i am planning on 2 characters now since you cant get 1 character to be supreme at all classes. i will put together engineer and medic then soldier with operative.

you lose 1 level for selling abilities then just earn it back again, You are still allowed to lvl 20

sweet. i just didnt want lose out!