I received a gift from a friend in the UK and I live in the US, so how do I redeem the gift, Because I'm not allowed to redeem?

You can't redeem it, you need to be in the same country as the sender and with an account based in that country. Your friend could try resending it to somebody else who has an account in the UK (resending gifts), or they could try contacting iTunes support and see if they will refund or credit him/her : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption