well somehow after i received my new micro sim the pin code wasn’t working and i always had to block my sim (3 wrong pin inputs) and unblock it with my puk. since i didn’t know the pin i couldn’t change it either.

i found out how to change your pin using your puk, just dial this number (works in emergency call or unlocked mode):
**05*<PUK Code>*<enter a new PIN>*<confirm the new PIN>#

you should receive confirmation that the pin has been changed.