Assuming you were sentenced within a few months after you changed your plea in court, your time to appeal ran out long over a decade ago. Furthermore, you cannot file either a state postconviction motion under rule 3.850 because there is a 2 year time limit on that or a federal petition for writ of habeas corpus because there is a one year time limit on that.
So, regardless of whether you have a viable argument for busting your plea, you have no statutory legal remedy available to you.
However, there is an outside chance a common law writ of error coram nobis MAY be available to you as a remedy.
You must consult with a Florida counsel with a great amount of experience in Florida postconviction procedures to see if you still have any legal remedy. You can find such counsel here on Avvo by clicking on Find a Lawyer at the top of this page.
Cal. Bar No. 104800
Wis. Bar No. 1020123
Member: U.S. Supreme Court Bar
Remember that even if you could challenge you guilty plea, that is a dangerous thing to attempt. If you should succeed you could find yourself back at square one, facing the original charge without benefit of your plea agreement. In other words, by withdrawing your plea you expose yourself to a risk of conviction and potentially to the maximum sentence.
So even if there were a way to do this, be careful about trying. You might succeed and be very sorry about it.