Ah fun. So, I have a webserver that I have to do a remote reinstall for. That's a challenge. But, the real challenge is that the webserver has only one partition. Normally, I would think that I could unmount a /var partition or something, and then install the new OS in there via something like a chrooted environment and some post configuration. Then modify grub and we're off to the races. But I've never done an online partition resize.
The documentation is unclear here. Some forum posts says that you can with resize2fs: