When trying to update I get this error:
Incompatible archive: PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature
You can get the updated pclzip.lib.php from SVN or !http://www.phpconcept.net/pclzip/ -- and copy it to your piwik/libs/PclZip folder.
Alternatively, you can manually update.
This was fixed in 0.5.3, so once you're on the latest version, future updates should work correctly.
well the workaround sounds good but isn't working! I tried the version of pclzip.lib.php from SVN and from http://www.phpconcept.net/pclzip/ but I still get the same error
There was a broken sendHttpRequest in early versions of Piwik 0.4.x. The patch is: http://dev.piwik.org/trac/changeset/1532/trunk/core/Piwik.php