Please see links below that might help you: (you are talking about 2013 version I guess)
Re-create a whole new file from the corrupted/bloated file:
1. Open a new blank project file
2. Go to Insert/Project and insert the problem file.
3. Select the first task which will be the insertion point summary line.
4. Go to Project/Task Information/Advanced tab.
5. Uncheck the “Link to Project” button and hit “OK”.
6. If the file isn’t already expanded, expand it.
7. Select all tasks below the top level summary line.
8. Outdent the selected tasks.
9. Delete the first task which previously was a summary line.
10. Save the resulting file.
Hope this helps.