DB upgrade procedure

Right now I've only got a handful of users so any upgrades to the DB are easy. With more and more users starting to use RDM, how would I handle upgrades to the DB?

Per the help, I would need to be the only user connected but I'm certain some users would forget and leave the RDM open or forget and try to open it during an upgrade.

Is there some SQL script where I could kill all connections and prevent new ones to a specific DB except for mine?

For users who don't upgrade their client, I assume the upgraded DB would still work for them (or should I simply set the minimum version to force them to update on next connection?)

Thank you