The key to a remote upgrade is to be able to boot from floppy disk to perform the upgrade, and then to reboot from the hard disk. The possibilities are:
Most BIOSs allow the boot disk order to be controlled through the BIOS' configuration. If the BIOS supports a serial console then the machine can be upgraded whilst leaving the floppy disk in the drive. No one need attend the site to upgrade the operating system
Someone can insert a floppy disk before the upgrade and remove it afterwards. Most co-location sites will provide this level of "board-swap" technical support.
Two records of the CMOS memory which stores the BIOS configuration can be made: one for booting from floppy and another for booting from hard disk. Unfortunately the nvram device driver does not yet work on a wide enough variety of machines for this HOWTO to pursue this option further.