Help Needed With Umbraco 3 CMS

Hi,

I am optimising a clients website, well I am trying to, but I cant figure out how to change the alt image tags, I have found where to insert the alt image tags in the media tree UI within Umbraco 3, but the changes wont seem to upload
and the old alt image tags remain in place on the website.
Anyone got any experience with this content management system ?
Any help would be appreciated.

Thanks, Nick.