User blog comment:Reinbow/League isn't the same as when I started/@comment-71.231.77.129-20130103120127/@comment-3475363-20130103134358

Go to the shop ingame, then click on "Purchased". You will see a list of purchased champions, runes, skins etc. Click the refund button and voila your IP/RP is back.

You can only use it 3 times though, so think before you refund.