This is the most common frustration. You type the IP, but the browser says "This site can’t be reached" or "Connection timed out." Here is the fix.
Once logged in, you will see the Mercusys web management interface. From here, you can change WiFi settings, update firmware, set parental controls, and—most importantly—change your WiFi password. 192.168 1.1 mercusys login wifi password
Not every Mercusys router uses 192.168.1.1. Some use 192.168.0.1 or mercusys.net.
Solution: Find your actual gateway. This is the most common frustration
If the gateway is 192.168.0.1, use that instead. Not every Mercusys router uses 192