Allied Telesis AT-S63 - Manual (Page 501)

AT-S63 Management Software Command Line Interface User’s Guide
Section VI: Virtual LANs 501
delete vlan=Service ports=2 frame=tagged
delete vlan=Service ports=6-8 frame=untagged
Using Syntax 2, you can do the whole thing with just one command:
delete vlan=Service untaggedports=6-8 taggedports=2