Upgrading Kupu in Plone is not that difficult.

First you need to download the latest Kupu files from:

http://plone.org/products/kupu

Then you should rename your old kupu folder to, for example, kupu-old. The default kupu directory is:

/opt/Plone-2.5/zeocluster/Products/kupu

(the version of your Plone instance may be different)

Extract the latest kupu in /opt/Plone-2.5/zeocluster/Products and then restart Zope.

After that log in to Plone and go to > preferences > Add/Remove Products. Under Installed products you will see your kupu version, as well as a message saying that the files have been upgraded. Follow the link to reinstall kupu and this will complete the kupu upgrade.