Upgrading on Wordpress is a straightforward task, however it includes one step that other Wordpress plugins don't normally have.
First of all, visit your Plugins page in the Wordpress sidebar, and click Update Now.
Next, and this is really important, to back to Jomres in the sidebar. This will trigger the complete update process, so when instructed click Continue to download the full package file of Jomres and follow the onscreen instructions.
Once you have updated, then you can update any plugins that need to be updated too.