I'm trying to remove the part of the frame that was holding the chainguard but there seems to be a kind lockring and I don't know which tool to use. Any ideas?
EDIT: I am referring to the topmost six-edge nut, NOT the lockring (I do have a C spanner for that.)
EDIT: I've accepted ojs's answer: the six-notch cup is the fixed part of the cup, it's not supposed to be removed at all unless the bottom bracket is completely replaced (and that was not my goal); the lockring is supposed to be removed without removing the cup. I took the bike to a mechanic who pointed out that this is a reverse-threaded cup, which I knew, however since the cup is reverse-threaded so is the lockring (it cannot be otherwise). The whole lot was seized and rusty (the mechanic had to hammer it a lot). Apparently I made things much worse but tightening it further while trying to unscrew it. Lessons learned.