In order to reset the VLAN information to the factory defaults, delete the vlan.dat file from the Flash or NVRAM and reload the switch.
On the Cisco Catalyst 6500/6000 Series switches running Cisco IOS Software, the vlan.dat file is stored in const_nvram. On the Cisco Catalyst 4500/4000 Series switches running Cisco IOS Software, the vlan.dat file is stored in cat4000_flash:. On the Cisco Catalyst 2940, 2950/2955, 2970, 3550, 3550, 3560, 3570, and 2900XL/3500XL fixed configuration switches, the vlan.dat file is stored in flash:.
In order to reset the Virtual Trunking Protocol (VTP) information when a switch is added to an existing VTP domain, the best option is to change the VTP mode to transparent. To do this, issue the vtp mode transparent command. This changes the config revision number back to 0 and when the current VTP server has a higher revision number then this, the device is updated with the latest VTP information.
Refer to Resetting Catalyst Switches to Factory Defaults for more information.