- Launch JCrypTool and open the preferences via Window - Preferences
- Expand the Install/ Update section and select Available Software Sites
- There should be one entry with the location http://www.cryptool.org/jcryptool/update
- Select this entry and click Edit
- Replace the location link with the new update site URL http://www.cryptool.org/jct/update
- You can give the update site a name optionally (in case this wasn't filled automatically)
- Click OK to close the dialog and OK to close the preferences
In case you are already using release candidate 5a (RC5a) you do not have to update the URL.