How Do I Change Text in the Legend of a Chart?

[FC]

    I use OpenOffice 3.4.1 with Windows 7 Home Premium 64-bit.

    I'm only an occasional chart maker.  I created a chart years ago,
of Column, Stacked, with three Data Sets.

    Will some kind person please remind me how to change the text
in the Legend for the three Data Sets?

    Fred