Okayyyy so you want to make a few changes in Manager well simply:
Start by going to the Campaign page.
Find the Creative Set you would like to preview
Click on the three dots on the specific Creative Set
Now click on 'Creative editor'
You now have your list of all the creatives where you can change between each creative and make your changes.
Now to change your image just:
Click on your image layer either in the workspace or in your layer menu
Go under Assets
Choose the new image you want to use
Click "Apply to all formats" under "edit" in your right hand menu
To change text simply:
Click on your text layer
Change the text in the workspace or under "Edit" in your right hand menu
Make the changes on all formats or just selected
And lastly want to change the clicktag in a creative set:
Go under "Clicktag" in your right hand menu
Insert a global clicktag and content specific if needed
And that's it... really that's it π