A judge can exercise their discretion in regards to whether they grant an inmates 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 inmates disciplinary report.
These are some of the documents to help you attain your new sentence.
Hiring a private attorney will gelp get your case to the top heap, and get you resentence much more quickly than if you wait for the government to sift through the eligible cases.