Problems when trying to update JMonkeyEngine

I want to update my JMonkeyEngine SDK, so I went to: Tools > Plugins > “Updates” > “Check for updates”.
I got a message window with two boxes of text:

Unable to connect to the Certified Plugins because of Connection reset

Check your proxy settings or try again later. The server may be unavailable at the moment. You may also want to make sure that your firewall is not blocking network traffic.

I clicked on “Proxy Configuration…” but I don’t know what to do.
Also when I try to update with Help > Check for updates I get the following message:
Checking for updates failed.
Check your network connection, verify that your proxy settings are configured correctly, or try again later.

How can I solve this problem? I really want to update because some things of the SDK have never worked for me. For example when I open the scene composer, the model viewer, vehicle editor the SDK keeps throwing hundreds of exceptions and freezes. I only can close the program then, and restart it.
I hope (some of) this problems will be solved if I update. But updating fails.
Thanks in advance for your help.

Check your internet settings for a firewall or a virus scanner where you have to allow each application access to the web. Your issues with opening the GL windows sound more like a graphics issue, like you only have windows update drivers for your graphics card instead of the ones from the manufacturer or have a graphics card that otherwise doesn’t support OpenGL2. See the troubleshooting section for that: