The process for recovering guardianship from grandparents will depend upon the reason that the guardianship was created. If you voluntarily transferred guardianship due to non-fitness reasons (such as an extended work trip abroad) and the grandparents do not object, you can file an agreed termination of guardianship. However, if the guardianship was involuntary due to your unfitness, you will need to prove at a hearing that termination of the guardianship is in the child's best interests.
Draft your petition for termination of guardianship. You can obtain a blank copy of the form from the clerk's office in the county where the child currently resides. Although the specifics vary by jurisdiction, you will need to enter into the petition the case caption from the current guardianship, the full information on the child's natural parents, the guardian, the arrangement and attach a copy of the current guardianship order to your petition. Include in the narrative the basis for your petition. If, for example, you were previously adjudicated as unfit due to drug use and have completed drug rehab (the basis for your petition), reference this in the narrative, attaching a copy of the rehabilitation report to the petition.
File your petition with the clerk's office of the probate or family court that entered the previous guardianship order. Serve the petition upon the other natural parent and any guardians currently appointed via a special process server such as the county sheriff. The court will have a status date on the petition, and if the parties cannot come to an agreement, set the matter for a contested hearing.
Appear at the hearing on your petition. This will be your opportunity to present your evidence and witnesses, and the current guardian will be able to present his side as well. The court will be guided by the best interests of the child, only entering an order modifying guardianship in your favor if you can prove this to the court by the preponderance of the evidence, because it is your burden to prove as petitioner.