This isn't as much of a guide as it is a simple patch I made for the game.

I made a quick mod to Final Fantasy IV to make the in-battle speed 20fps instead of the default 15.
The reason I chose 20 rather than 30 is because (as of yet) there's no way I've found to increase FPS while at the same time maintain the battle speed, so 20fps is a bit of a compromise.
The only thing the patch does is change a hexadecimal value from 0F (15) to 14 (20).
I hope you like it :)

(Patched for 25fps)

Download this file and replace the original file in the game's folder:

20fps[1drv.ms]

25fps[1drv.ms]

The file is usually located in:
"Steam/SteamApps/Common/Final Fantasy IV/FF4.exe"

• Download a hex editor of your choice.
  
• Change value from 0F to 19 (25fps) or 14 (20fps) in the following locations, and keep in mind that these are addresses and not actual text inside the file. (FF4.exe)
  - 000A2FA5
  - 00111EFD
  
  
• Save the file

2024-08-13: Updated download links again
2022-10-09: Updated links to not use google drive any more
2020-11-08: Updated offsets and binary so it works with the new update! (Thanks TiresomeTeddybear!)
2016-01-02: There's possibly a difference between EU and US versions, I added new offsets for the US version (if that is even the case, some people have other checksums on their game for some reason)
2015-05-12: Fixed a bug where the FPS would drop back to 15 after an eidolon had been summoned.