The game uses Autodesk Scaleform to display UI graphics and HUD elements on the screen.

Button prompts are both stored as scalable vector images (SVG) and defined inside Shockwave Movie Files (.SWFMovie) as 'sprites'.
On the other hand, texture images (usual DDS textures) for UI/HUD (think menu icons, controller picture in options menu) are stored outside SWFs but defined inside them as sprites to be displayed on the screen.

As a result, there are dozens of layers of this Scaleform tech which display different collections of elements on the screen.

There's a different layer for button prompts that appear on the bottom right (use gadget's primary fire/secondary fire) and left (gadget selection) than the one that appears in the middle (tutorial prompts like hold SPACE to run, CTRL + SPACE to open a manhole or ground vent, and prompts for predator takedowns and the subsequent tutorial texts that correspond with them).
Likewise, there's entirely different layers for each menu (Riddler trophy menu, WayneTech upgrade menu, maps/objectives screen) and HUD elements (health bar, compass, name that appears at the top when entering a new area, detective mode).

So, UE Viewer is needed to export these SWFs (or GFXs, they're both the same thing) from the game's UPK package files.
After that's done, to decompile those SWFs a Flash decompiler will be needed (JPEXS FFDEC is the best in my opinion), using which you can remove/edit the definition for the sprites (text, button prompts, menu icons, HUD elements like gadget wheel, compass, objective marker, broadcast analyzer, health) that correlate to the elements that you want removed/modified.
Then use UPK Explorer to import the edited SWFs and create a game patch which can be injected into the UPKs using TFC Installer.

For aiding user BatmanArkhamForever with his mod to remove tutorial prompts, the files related are most likely BmGame.upk and Playable_<PlayableCharacterName>_SF.upk. Look for SWFs with names along the lines of HUD, FrontMostLayer, Image. They contain the definitions for the text and button prompts accompanying the tutorials.

The font styles for the Arkham games are stored within SWF files.