Hello rodrigovenegas,
There is a logo file for each and every theme of your template. Have a peek into for instance:
templates >> ja-methys >> themes >> red >> images
– there is probably a logo.png file that you need to replace, as in the remaining theme folders.
Add to that a (default) logo.png file in the templates >> ja-methys >> images folder.
Look out for other logo filenames as well; you may find a logo-trans.png when the template logo is a negative as is the Methys logo.
The logo.gif file you have replaced is probably the Joomla! logo. The naming convention seems to be .gif format for Joomla! logo and .png format for the template logo.
Hope this helps and good luck with your site!
Steinar.
