You need to upgrade or install a new system. As you can see at the Linux Mint link below, Mint 9 has not been supported since April, 2013. Mint 13, 17 and 17.1 are currently supported and 13 and 17 are long term support.
The link below has some explanation of upgrading Mint, pros and cons. It would be easier to do a new install which they refer to as a "Fresh Upgrade".
The link below is to the download site for the three supported version. You will be better off with 13 or 17 as there is longer term support. There is also a KDE version for each if that's what you want.