The solution is not as difficult as it seems ...
Do the following, you do not need no computer, no cables, delete or anything ...
1. Back up your contacts to the SIM (Menu / Contacts / Options / Back up SIM card.)
2. You have to reset your phone ... Settings / Backup and Restore / Factory data reset ...
3. Ready! There is an option that puts you to delete all the data, that's not marques and ready.
Your phone and stayed with the new android, flawless and all that was lost was the call log, messages, and obviously have to re-install the applications you've downloaded.