To upload your own branded font, start off by clicking 'Integrations' in the sidebar.
Once you're there, just click Fonts and choose the TTF option (blue document icon).
IMPORTANT:
You must have the necessary rights/license to use the font
Only .ttf files are currently supported.
You will need to upload each font file separately. For example, you may have one for Regular, one for Bold and one for Italic.
Click 'Upload a Custom Font', enter the name of your font and below this, you will upload each file that your font requires.
Click 'Browse for Font' and upload the first file. You'll see the file name appear in the 'Font File' field. Now select the correct weight and if it is an italic font, tick the 'Italic' box.
You can add more files by clicking 'Add New Row' and then click 'Save changes' once you're done.
You can now select from your custom fonts in Font settings - hover over your profile picture again, click Settings, pick the brand you wish to edit under ‘Branding’ and find the ‘Fonts’ tab. You can read more about font editing here.