FreePBX doesn’t install Asterisk. If you used a distribution like PBX in a flash (The official FreePBX distro was not around back when you installed) you have to use the instructions for that distro.
If you installed it from scratch you have to upgrade Asterisk by downloading it from asterisk.org and installing.
Also, pay attention to the other requirements of FreePBX 2.10 for PHP.
If you don’t have a complicated system I would start from scratch. You can backup your greetings and such and restore them. Nothing else is compatable.