The firmware update can be done with some delicate (!) soldering skills.
By removing the flash chip U1 from the motherboard (It's on the back so you'll need to completely remove the motherboard from the scope), you can place it in a chip programmer like the xgecu TL866II Plus with a TSOP adapter (and 8-bit carrier board) and flash the new firmware.
However, as this flashes the entire chip, you will then need to recalibrate the instrument, after doing a full factory reset, SPC, etc.
You can find the firmware images here, the latest for the THS720A, THS720P and THS730A is 1.16 (they all use the same firmware):
https://w140.com/tekwiki/wiki/THS720
Note, DO NOT mix firmwares between the THS7XXSTD/THS7XX and THS7XXA/THS7XXP models, they are not compatible due to hardware differences!
I have done the upgrade to a number of THS700 series scopes, but it does run the risk of damaging the motherboard due to the desoldering and resoldering of that flash chip, so proceed at your own risk!
I'd love to get documentation on the internal connection (or get my hands on an original programmer) to figure out a way to flash the firmware in a more safe and 'official' way, but such is life...
