The process for managing group filters has changed since ServiceNow was upgraded to the Helsinki release. These instructions cover the changes.
The previous way to manage filters was by clicking on the "Manage Filters" button at the top right of the "Load Filter" window. If you select this option now, it may appear that you have no, or substantially fewer filters than you expect. This is because this resulting list shows all filters in the system, and yours are likely not listed on the first screen.
We have a new, better option to mange filters. Two menu items have been added to the "Self Service" application under the Application Navigator: "My Filters" and, optionally "My Group Filters". The second menu item will only be visible if you are sharing filters with your group or someone is sharing filters with you.