Double check to make sure nothing is being blocked in your firewall.
Double check that your antivirus is not stopping osu! from updating. You can temporarily disable it, however do this at your own risk and be sure to enable it as soon as you are done.
Release/Renew IPConfig and flush your DNS
Restart your Modem & Router
If none of the above steps work, navigate to your osu!\Logs folder and provide your update.log.