How to edit pivot table data source??

I have a pivot table object embedded in an Access 2003 form. The data source
for the pivot table is a table in the database. How can I edit the query for
the pivot table? To use the pivot table it activates Excel. When I then go
into the pivot table wizard the Back and Next buttons are disabled.
Essentially, all I can do is adjust the format of the table. What am I doing
wrong?