Hello,
If you are referring to the "Powered by ResourceSpace" logo in the simple search area it is possible to completely disable it by adding $show_powered_by_logo=false; into your config.php file. If you're comfortable changing code you can edit the file include/searchbar.php, search for the class "PoweredByPanel" and change the "href" attribute of the hyperlink within to the URL of your choice.
If instead you were referring to the "Powered by ResourceSpace Open Source Digital Asset Management" text on the login page you should visit the following page: pages/admin/admin_content_edit.php?page=all&name=footer and again change the "href" attribute of the hyperlink.
Best regards,
Joseph