The integrated OSD feature on Betaflight boards like the Omnibus F4, or Betaflight F3 is that you never have to update the OSD firmware. However, I have been receiving a few support requests saying that the OSD font cannot be changed. So here is a quick guide to how to do this properly.
Update to the latest stable version of Betaflight
The first thing you should always try if running into difficulties to make sure the latest firmware version is being used. As often new firmware releases will solve a bunch of bugs in the code.
How to change betaflight OSD
To change the font you simply need to connect to your board with the BetaFlight GUI and go to the OSD tab.
On this screen you can edit the layout of the OSD, however on the bottom right of the screen you will see the Font Manager button that you need to click on. A new window will open with a bunch of built in fonts that you can use. If you are all for style, you can change it to a cooler 
looking font like Betaflight, or Digital. If care about having the data in your face (or its too hard to read 
), using the Bold, Large, or Extra Large font will be best.
There is also an option to use a custom font, but unless you know what you are doing it will not work.
Once selected press the Upload Font button, and you will see the progress bar showing the font is being written to your flight controller.
Once complete, the your flight controller will reboot. Now you can start using your new OSD!
Betaflight does not update font in preview
One point of confusion, is that on some PC’s or flight controller when you update click between the different custom fonts the preview screen changes. But after you write the firmware to the board, the font preview within the betaflight GUI reverts to the default. So one would assume the font update did not work? However if you connect up your FPV gear you will infact see the new font is being used. Its just the preview in betaflight that does not work.