Microsoft Licenses

Hello Experts,

Is there a way to re-key Microsoft licenses (Windows, Office, SQL, etc.)?  For instance, all our servers and workstations were built with VL keys for all sites (A, B, C, D, etc.)... now, we're selling site C, but can't transfer the licenses... is there a tool that I can remove the license keys from all machines?  Or what is the correct way to do this besides reformatting them?  Thanks.