To change the logo size, please go to admin->theme options->header->logo and change the logo height.
And for the font problems, you can also change your fonts on theme option panel->Typography.
After change the theme option panel, you can't see the changed result on front-end.
Because the problem is caused by browser cache.
At that time, please press "ctrl+F5" on your front end. Then, cache will be clear and you can see the changed result.
If you have any other questions, please let us know again.
Best Regards, C-Themes