In some cases you do want to make a change to a report you have created and might run into a message like this: "You have chosen to edit report "xxxx". This report has saved copies. Do you want to edit the report with limited editing capabilities?".
This means that you cannot change the definition of the report while there are still "old" copies. To resolve this you have to first remove the copies before you can do your changes. To do so, login as a user who has the rights to change the report and open the report itself (not in edit mode, open it in view mode). You will see, as shown in the below screenshot, the number of saved copies.
When you click on the number you will be guided to a page like the one below:
You will have to delete all saved copies of this report. When you have done so and you enter the edit mode of the report again you will see that you have full editing capabilities and are able to make all changes required.