By default uninstalling Jomres does not affect the existing Jomres tables, this allows you to re-install Jomres at a later date whilst maintaining the original data.
If you want to completely remove Jomres altogether you will need to visit Jomres > Settings > Site Configuration > Misc tab. In there is an option "Delete all Jomres data when uninstalling?". Set that option to Yes and click Save. Once you have done that then you can use the CMS's uninstallation process to uninstall Jomres entirely.
If Ioncube isn't enabled on your server
If, for one reason or another you can't or wont install ioncube on your server and you have installed the plugin manager as part of a trial installation, then you will need to make an extra step first. Using FTP navigate to the /jomres/core-plugins directory and delete the subdirectory called "plugin_manager". Next, empty the /jomres/temp/ directory.
Once you've done that you can then go back to Jomres in the administrator area of your CMS, go to Settings -> Site Configuration and set the "Delete all data..." option to Yes and then use the CMS's uninstall feature to completely get rid of Jomres.