You can uninstall using gL-Inet GUI, LuCI or SSH. Depending on you set up it might be best to revert your modem to factory, which is what I did and then uploaded a config file, after unistalling reinstalling adguard for a hour because it backs up itself in virtual memory. You will need to restart the router after each uninstall of adguard as it saves things in Virtual memory.
Here are to more post with useful adguard infomation.