In the 802.1Q VLAN page you can enable/disable the tag-based VLAN function by clicking (Enable) or (Disable) besides the page header:
¾Enable – to activate the tag-based VLAN function (port-based VLAN function will automatically be disabled).
¾Disable – to de-activate the tag-based VLAN function, even though there are some VLAN entries created. (i.e. any tag-based VLAN entry is still retained although tag-based VLAN function is disabled. Port-based VLAN function will be auto enabled.)