You can use Save or Save as... at 300 dpi for your personal files.

For posting on the web I use Adobe Photoshop CS2 for re-sizing.
If you use Photoshop it's real easy.
In Photoshop click on the Image tab, scroll down and click on Image Size.
A pop up screen will appear. The screen capture is of your image:

You can change the resolution & size to reduce it. For Resolution: I use 150 dpi with a height of 11 cm for match covers on thechipboard.
When saving I choose the Save for Web option for posting.
Your image is 1.17 MB in size while my choice is 57.5 KB.

This is 57.5 KB in size at 150 dpi and a height of 11 cm:

This reduced size should load pretty FAST.