You are getting confused now. Let me explain you in detail:
1) If you want to start Upgrade GUI in browser, then 2 ports are used
HTTP port/GUI Port: 4239 and SL controller port: 4241
2) If you want to start upgrade GUI with DSUGui command then in addition to above 1 more port is used
srvarg=/DSUService/abaptoolport=<port number for ABAP update tool>
I hope it will be clear now.
Thanks
Sunny