All stored assets in QBank can be edited after upload. You can both edit the image it self but also all the attached metadata.
When you want to edit an asset in Qbank simply select the asset you want to edit and click the edit button which is located in the toolbar (or use the hotkey "e").
If a single asset is selected, the "edit media" dialog appears.
All property fields of the asset is displayed with current values. Some fields (properties of list types) have the "View tags" button.
When clicked you'll be presented with a list of tags that's already in use by other assets. This is handy if you need suggestions of tags that others has used before.
Edit the metadata you want to edit and press save.
You can also edit the asset itself. For example you can upload a new version of the image or you can use the Image Tool to edit the image itself.