Firstly we recommend checking if you are running the latest version of OptimizePress. You can do this by checking the "themes" page within wordpress and you will see a number next to the OptimizePress logo. Now go over to your members area, and check the latest version number available. If the version inside the members area is more recent - download the file.
Now follow this guide for the full step by step : http://www.optimizepress.com/training/installation-updates/update/