To uninstall Jomres you can use the CMS component uninstaller, but note that depending on how your web server is configured the web server software may not have the correct permissions to remove some files so it's always wise to check the /components/ and administrator/components directories after performing an uninstall to ensure that the application's sub folders have been removed.
You will need to manually remove any Jomres related files in the /jomres directory.Typically this would be through FTP.
Jomres does not modify any tables during the uninstall process so you will need to manually edit your CMS tables to drop those created by Jomres. They are easily identified as they use the pattern XXX_jomres_XXXXXX, XXX_jomcomp_XXXXXX or XXX_jomresportal_XXXXX.