Sorin, you have not indicated which fonts for which objects you wish to change.

None the less, assuming you wish to use an websafe alternative font, go to any text object and select other font types, select add and I strongly recommend google fonts.

Once you have your font go to step 2 template, text field and button style and set your chosen defaults. Much text will change automatically, but in many cases this will not change the existing text font, but it will change all new text you add to your project.

Now go to each object with the wrong font (eg page text) block and select your font.

Be aware that some objects (menu, description of photos in galleries, etc) have their own text font and size menus.