Hi Rafael,
LEDs turning on and off from WAN to LAN1 in sequence means the router is in BootLoader mode. You can close the browser window after you see 'Update in progress'. The update itself takes only a few seconds but the router will restart afterwards. The entire process before the router becomes reachable again will take 3-4 minutes. Have you tried to reach the router after waiting some time?
Also don't forget to change back your PC's IP address because it might cause problems when connecting to other devices or no internet access if you haven't specified any DNS servers manually.
Which bootloader version do you have btw?