How to change a text's font?
To change the font of a text, you can:
Select the text layer (in the Layer List on the left, or directly on the canvas)
Click on the Design tab (at the top of the Property Panel on the right)
Change the value of the Font Family property in the Property Panel.
How to upload a custom font?
You can also upload your custom fonts on Jitter. To do so, follow the steps 1, 2 & 3 listed above and:
Choose "Add custom font" in the font's pannel
Drap & drop or upload your custom font file (.otf or .ttf)