You can obscure it with a blur or mosaic, very popular techniques these days, but there's no way to make it disappear without cropping it out of the shot. If you're using someone else's footage, maybe you could ask them for the original, without the logo.
> I´ve tried the stamp tool but it doesn´t work on footage.
I don't understand this comment. The Clone Stamp tool works on video footage; that's what it's for.
Here's a video that shows how to use the Clone Stamp tool:
I assumed he was trying to use a stamp from Photoshop.
I've never tried to removed something as big as a watermark using the Clone Stamp. I should think that would be painfully obvious but so is a blur or mosaic.
I just needed to press the footage two times to work on it!
Sometimes you need to take a deep breathe before stressing with the work.
Thanks for your answers.