I made a custom report type . I included a few objects and related them using object relationships which was correctly displayed in the set (Venn) diagram . However , the fields of these objects are not available for editing in the edit layout detail of 'Fields available for reports " section. The fields are visible but am unable to make changes to them . Please help.
This is somewhat tricky and is explained well here.
Go to Setup -> Create: Report Types -> Click on the Report Type's Label -> Click "Edit Layout" within the "Fields Available for Reports" box on the right, you'll see the "Field Layout Properties" section.
You can drag and drop desired fields to this layout. If a field you wish to include is not visible under one of the selected objects, you may be able to add it via lookup.
To do this Select the respective object from the "View" drop down field on the right side of the page. Click on the "Add fields related via lookup »" link directly below the "View" drop down field. Select the appropriate link and subsequent fields. Repeat this process as needed per object.