Change default phone number in Pytheas theme

Hi, I would like to ask how can I change the default phone number that comes in Pytheas theme on the upper right corner. I tried to change it in header.php in the editor and saved it, but nothing changed. Is there another way?
https://www.wpexplorer.com/pytheas-free-wordpress-theme/

Also I would like the portfolio slider in this page
https://wpexplorer-demos.com/pytheas/portfolio/designs-slider/
to make the images fit into its with and height instead of clipping them.

Thanks a lot.