Please check status of the abstract. You can not modify it if it has been accepted by PGC.
If status is not "Accepted", you can modify it following the steps:
1. Click the title of your abstract and browse corresponding abstract;
2. Select the type of your operation (Edit of Delete), the click "Execute";
3. If you chose "Edit", you can modify cantent or style of the abstract in the new page. Then click "Update" to finish it.