On your WiFi connection settings long press the wireless network (the one with the proxy) and it will prompt you to either 'Forget' or 'Modify'. Click "Modify" and then tick the "Show Advanced Options" box and it will show you proxy settings for that network. If that doesn't do the trick then try looking for proxy management apps or VPN apps (bypass proxy completely). I'm sure there's at least a few of those out there.
Nexus 7 (2012)
Sony Xperia SP C5303