Like Yves suggested you will start the SUM tool under the sidadm user.
If you want to upgrade both the systems at the same time then you need to start the SUM tool twice but you need to make sure there are two different SUM directories (one for DEV and one for QAS)
To start multiple upgrades in parallel then you need to start it with different ports. This is clearly mentioned in the SUM guide. Please read the SUM guide for details.
NOTE
If you are running several updates in parallel on the same host, you have to use different port numbers for each. When you start the Software Update Manager, specify the port numbers
httpport=<http port number>
guiport=<GUI port number>
-srvarg=/UseCaseService/abaptoolport=<port number for ABAP update tool>
./STARTUP httpport=4538 guiport=4536 -srvarg=/UseCaseService/abaptoolport=4534
Regards
RB