What do software do you have?
With iMovie 09 you can make a title above (and maybe if you search more a title below). Just place your text, and copy, or stretch it over the entire movie.
Then export the movie.
If you have FCP (I guess you don't) go to your browser, filters, generators, text. Type in your text, drag the text from the viewer in your timeline above the clip. Stretch it over the entire sequence. Then export the movie.
I don't think you can remove a "baked" (that's the method I told you above) title. Cause there's no longer any material saved about what's behind the text. (something like filming your television, holding your hand in front of it, you can't get the information off what's behind your hand on the television).
maybe they meant that you have a trial version of software, and remove the marked copyright by filling in the serial key.