Did you mean RM-U306B remote? If so, the command code cannot be changed on the remote.

This remote is used on the STR-DE597 receiver, and information on that receiver will apply and is posted in my Receiver thread [Link: remotecentral.com]

On the remote (except STR-DE997 and STR-DE998): (You cannot change the Command Mode on the STR-DE597 or STR-DE598 remote, so if you want to learn any commands from that remote, leave your receiver set at AV2. You will have to learn everything because you cannot use any preprogrammed codes on your universal remote with this setting. If you don't want to learn anything, or your universal remote doesn't have learning capability, you can change the receiver to AV1 and use the universal remotes programmed codes.):
1. Press AV1 or AV2 while holding down RM SETUP
2. The indicator flashes once (twice for AV2), then the command mode switches
3. To check the command mode of the remote: Press RM SETUP. The indicator will flash once for AV1 and twice for AV2.