It has been a few years since I last worked on a C-More, but my recollection is that you can't change the data type of a tag that is used on any page. If you know where the tag is used you can change each usage to a different tag, then modify the original tag, then change each usage back to the original tag. Quite often it's just as easy to create a new tag as kamenges suggested, but if the tag name is particularly meaningful or specified by an end user naming convention you may want to keep the original name.