Please follow the upgrade instructions in the GreenHopper Installation and Upgrade Guide.
There is one known issue with this release. If you have the GreenHopper Night Service enabled under General Configuration please disable this prior to upgrading, full details can be found in this knowledge base article.
In addition to the above, please read the GreenHopper 5.7 Upgrade Notes and the Upgrade Guide for every version you are skipping during the upgrade. The complete list of Upgrade Guides is available here.