Removing a Rounded Edge with the Fill Tool
This method removes the rounded edge and creates a round group in the Groups panel. You can right-click the group and select Reattach Round to restore the rounded edge.
- Click the  Fill tool in the Edit group on the Design tab. Fill tool in the Edit group on the Design tab.
- Select the rounded edge. 
- Click the Complete tool guide. - The round is removed and a round group is created.