HELP. HOW TO LOOSEN JOINTS? ESPECIALLY ON ROBOT HEROES.

just recently got the prime robot heroes that come with the dvd.... but his right are is stcuk to his body that i cant turn it.... i tried to turn it with force thinking maybe that the plastic just stuck together because of sitting so long in the package. but it wasnt budging at it came to the point were i was twisting the plastic peg that holds the arm to the chest. if i continued more i wouldve twisted the arm off of prime
. so does anyone know any techniques on how to loosen stuck joints?
