Here are som instructions on how to redeem your key.
1) Access the site: http://www.runescape.com/store_locator
2) Log into your RuneScape account.
3) Enter the PIN code obtained in the indicated field and click on redeem
4) A message informing you that your Prepaid code has been successfully redeemed will appear.
It would be great if you could vouch for me once you have purchased!
NOTE! These keys cannot be used on an accounts that has an active membership purchased by card. Any other form of membership (bonds, pre paid cards or other) will be fine. If you have any questions or issues feel free to message me on here.