That would depend on how you installed the original system. To go forward you will need to update to Asterisk 1.8 either from source or from your installation whatever that is.
It’s been so long since I did the original install, I can’t recall exactly how I did it, but I’m pretty sure it was from a package of sorts - maybe even a complete machine install.
I don’t have a specific need right now, but I see I am falling behind in the releases, so I thought it best to upgrade at this time. In further searching thru the web, I did find one post that speaks about using “yum” to remove asterisk, and install asterisk18, but I don’t know if that will preserve existing config files.