How to update dedicated server?

I try to launch my server, then it shows “Your server is out of date. Please update and restart.” So i try to update it, says “I don’t need to download anything”. Can anyone please help me?

You need to use SteamCMD, not hldsupdatetool

Elaborating on what he said ^ https://developer.valvesoftware.com/wiki/SteamCMD

Thanks.