Due to some security and reliability concerns, System Administrator rights are restricted to Atlassians only. Specific customers for a particular instance can be granted "Administrator" privileges which are sufficient for them to manage its content.
Hope that clarifies your concern.
If you're missing things in OnDemand, then I'm afraid you are stuck - As Abdoulaye has said, OnDemand has limitations that the downloaded products do not. Atlassian are working on widening the range of things you can do as an owner.
You need to talk to OnDemand support to do what you need, or (as I'm not 100% clear what access you have) get them to add you to all the groups that you might be missing.
You may want to have at the below links regarding plugins installation restrictions:
We are sorry for any inconvenience.
Hello! My name is Genevieve Blanch, and I'm the Marketing Manager at RefinedWiki, creators of apps to give teams the tools to customize Atlassian platforms. Currently, 44% of the tech team at Re...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs