I need help improving my singing range?

Ok I'm only 14 but I need to improve my vocal range, I am in a choir and I sing anything from the higher tenor notes, all the way to the really high soprano and I've never had any problems, but now I'm a lead singer in a band and they are getting frustrated because I can't hit the notes such as like Livin' on a Prayer by Bon Jovi without going into head voice... I already know how to make the sound come from my diaphragm and not to just sing from my throat in order not to strain it... and I am slowly improving but I wanted to know if there are any tricks to help it happen faster? Pleasee help