Open "All My Books",
Select "Tools" > "Preferences" > "Expert Options"
Uncheck "Store all the images inside the Database"
(Wait for the program to move all of your images to a separate folder.)
Go to "Database" tab and then select "Compress database"
(Wait for the program to check and compress your database.)
When the compression is completed the program will display the size of your compressed database.
How big is your database now?