Yes, it is possible to rename the groups in a Pivot table. Here are the steps to do so:

1. Click on any cell within the Pivot table to activate the Pivot table tools on the ribbon.
2. Go to the "Analyse" or "Options" tab (depending on your version of Excel).
3. Click on the "Fields, Items & Sets" dropdown and select "Group" from the list.
4. In the "Create PivotTable Group" dialog box, you will see the existing group names (Group1, Group2, etc.).
5. Click on the group name you want to rename and then click on the "Rename" button.
6. Type in the new name for the group and press Enter.
7. Click on the "OK" button to close the dialog box.

Your Pivot table will now display the new name for the group instead of the default "Group1", "Group2", etc. You can repeat these steps for any other groups you want to rename.