How can I removed glued-on flowers...

Set your hair drier to medium-high heat and hold it a few inches away from where the flowers are attached with the glue. The heat will loosen the glue. After about 10 to 15 seconds, carefully peel off the softened glue. If any residue remains, depending on the fabric of the hat, you may be able to remove the stickiness by applying a little vegetable oil and rubbing it away.