A judge can exercise their discretion in regard to whether they grant an inmate's request to resentence. It is not an absolute right!
One of the things an inmate can do to help their attorney with the motion to resentence is to get a copy of any rehabilitative efforts (e.g. rehabilitation, drug rehab, firecamp, GED, etc.) and a copy of the inmate's disciplinary report.
These are some of the documents to help you attain your new sentence.
Hiring a private attorney will help get your case to the top heap, and get you resentenced much more quickly than if you wait for the government to sift through the eligible cases.