Unfortunately, you will not be able to update your S2 without using a PC or laptop. ICS is not (and never was) available OTA. As you are now behind on updates Kies may not even update you to ICS (depends which GB version you are on, if 2.3.3 theres little chance). Your only option is to use Odin and manually flash your phone with ICS or JB. If you cannot access a PC to do this I suggest a local phone repair shop, they usually charge around £20.00 for the service.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion. This is not Customer Service so we are unable to help with account specific issues.
Please select the post that helped you best and mark as the solution. This helps other members in resolving their issues faster. Thank you.