Alright, once situation is clearer - another important question:

I already bought "BB30 to Shimano adpater" from Rotor (link here) , so is it better to install this in the existing aluminium retainer that is still in the frame, or should I press retainer (cups) out and buy another adapter (in that case "PF30 to Shimano") to go to frame???

Background: I bought this used frame and came with BB setup like this. Seller didnīt mention any problem with BB, but since I really wanna have Shimano groupset, I need to go this way so I can fit 24mm spindle of crank.

Any thoughts?