To update your PRL (preferred roaming list), you should dial *228 and select option 2.
The update will only work if you have an adequate signal to download it, however.
Did you lost signal recently? If going to an area with a signal and reprogramming your phone doesn't help, you should call Verizon's CS line (check the "Contact Us" link at the top of this page) and dial option 3. That will connect you to tech support, and they can troubleshoot and possibly file a trouble ticket if the issue is with the network and not your phone.
All these things have been done to no avail. Called tech support 6 times I went to the Verizon store twice my phone has been updated by me and tech support. I was finally told that a tower was down in my area (Hampton). Are they going to ever get it fixed. I need "CAN YOU HEAR ME NOW" service that I use to have no more LOST CALL!