Yes, this is possible, however, not while CentOS is running. You will need to boot from a live cd or other live boot method, and then partition from there, so the system doesn't use the disk for other things.
This may be more difficult on a remote server, if your hosting company doesn't support live environments, then you will have to do more complicated (and potentially dangerous) things like booting your OS in RAM, or making Grub2 boot an ISO in RAM, where the ISO has to start a ssh session on boot, and set the right ip. If you do this incorrectly though, you may end up with an unbootable server, and have to wait for your hosting company's support.
If you want to know what programs to use to partition it, you could look into
gparted for a non-headless system, or
parted for commandline tools. Resizing with the latter 2 tools is a bit harder though.