You can not install OpenKM with cpanel. For installing OpenKM you need root access to the computer, because it is required to install several packages and services. If you have a VPS ( usually it comes with CPanel ) you need one with root access level, otherwise can not install OpenKM.
Please take a look at the video
Finally I suggest about 2 cores and 4GB of ram to run OpenKM if your VPS do not have at least this configuration I suggest upgrade.