Is this a server used for the actual school site? As in for the public to see district information, or is this something like a project server for the high school alone?
I see a couple options. If the machine is older, now is the time to evaluate whether to replace it and rebuild with more storage and memory and a warranty that covers parts going bad. Or you could look at getting a decent server that runs VMWare ESXi or some other virtualization so you can run the web server under a VM, which can make it easier to transition to another server down the road if you needed to (or add redundancy by getting a full package for failover between two or more virtual servers). Plus you can back up the machine from "bare metal" by just copying the VM image if need be, or making sure you have a good backup agent intstalled.
Second, you could check and see if there's crap in it that should be deleted. If the server isn't all that old, what the heck is taking up all the space? Old log file? Are people uploading 100 meg JPG's or movie files? Do you have files that are a couple years old that can be archived and moved off the server? Are you storing things from people that graduated years ago?
Third, make a full backup, replace all the drives, and restore the machine back. To some degree you should have a system in place for this already, as part of your disaster recovery/backup plans. Make sure you can restore from bare metal, replace all the drives and go to town with replacing the data and run it again on the old hardware.
Fourth, replace the server with a new one, migrate just the stuff you need, and unveil the new and improved server with old cruft removed after rebuilding the web server and template from scratch. Great way to start new. Plus if you didn't have things like backups properly in place, this gives you a chance to fix that. RAID is not a backup.