Go onto their region version of xbox.com, sign in then redeem from there
for example:
If you are in the US and what to redeem a UK code go on www.xbox.com/en-gb
and
If you live in UK and want to redeem a American code go on www.xbox.com/en-us
If you live in America and want to redeem a Japanese code go to: http://www.xbox.com/ja-jp
Ireland go here www.xbox.com/en-ie/
hope this helps
for example:
If you are in the US and what to redeem a UK code go on www.xbox.com/en-gb
and
If you live in UK and want to redeem a American code go on www.xbox.com/en-us
If you live in America and want to redeem a Japanese code go to: http://www.xbox.com/ja-jp
Ireland go here www.xbox.com/en-ie/
hope this helps