You can log into phpMyAdmin from your cPanel. From there:
1) Click on the table icon next to the database name you are working on
2) On the right hand column your tables should be listed. Scroll down till you see the “Check all” link.
3) Click on that link, make sure all database tables are checked and then from the dropdown next to it, select “Optimize table”.
This command will not work on all table types.