Can I just delete leases in DHCP to force a new lease on client?
Solution 1:
That's a bad idea. They won't try and renew the lease until it is expiring. Deleting the lease will cause other machines to be able to get that IP. What you want is either to run ipconfig /renew via psexec or to script the renew in PowerShell and run it remotely.
Alternatively, if the users reboot they should get the new configuration options.