How to unlock more slots for enhancements?

[rimean]

How can i do that? I've 2 slots locked besides having 11th lvl

[ARTSQ]

So, there's an enhancement called versatility that opens those 2 slots, but occupies one. So that basically means that you're opening just one slot.
it is a very situational stuff, since it's quite hard actually to get more than 5 enhancements (one for each level + starting one), since you need to visit "?", get the right event and then also get lucky enough with roll to get it.
Word of advice - don't sweat it. Usually you're getting either weak buffs like periferial vison, situational like Fast Learner (which is useless on last stage since there're no shops) or money-related (same story with the last level). So In vast majority of playthroughs chosing which enhancement to discard before last level is a no-brainer. Especially if your deck is fosued enough.
E.g. let's say you're playing deck draft and you're getting "+25% block" as a starting enhancement. But then your first draw and all rewards are very agressive-focused or dodge and movement focused. That would meant that you're most probably not holding any block cards, which renders otherwise usefull enhancements totally unnecessary for the last level.