[abusharif]

use central. Local is the old and non-recommended way nowdays.
You use ip# of the smartcenter server.

You download the license you created (central license, licensed to ur smartcenter ip). Then use smartupdate (license management part is free to use). Import the new license you created/downloaded into the smartupdates repository (you can find it in smartupdate menu). Attach the new licenses to the gateway in the same gui.

sidenote: If u reach ur limit on changing ip's and get blocked on usercenter, lock can easily be removed by dropping a mail to checkpoint.