To the right of the first row of tabs there is a drop down arrow that opens all the tabs once it is clicked and you can see all the tabs hover over the one you want to change and you will see a pencil icon click on that and you will be able to make your edits.

@safinaiqbal It depends on what the app is to edit content. The default first app is always the Photo tab and the image displayed depends on the most recent photo uploaded (there is no way to change this as of right now). The ability to edit any content is up to the app developer and if you are able to make any adjustments it appears in the edit tab that  @scottmadden mentioned.