I am 14 about to be 15 and me n my boyfriend are thinking about having .(help)?

My boyfriend is 17 and im 14. i am a virgin but he is not we are thinking about having and we r going to use a condom. My boyfriends is bigger than average and i mean biggerr.Dose any one have any advise on how we can make it less painfull because he is quite big and i dont want it to be an unplesant exeperience...?please help thank you.