We're aware of this problem, and are trying to resolve it. The resolution will likely require reinstalling.
Until then you have 2 options:
1. Reinstall, performing a full cross platform installation, per these instructions.
You should be able to update thereon without a problem, per these instructions.
2. Update your current installation manually as follows (but note you'll need to repeat these steps each time you update):
For best results, use the Firefox browser..