You will need to find the ISO file for Mortal Kombat: Unchained.
Use search engines with caution. Safe keywords include: mortal kombat 9 ppsspp iso download install upd
Red flags to avoid:
Since you cannot "update" to access DLC characters like Freddy Krueger easily, use PPSSPP's built-in cheat engine: You will need to find the ISO file
Note: This is not a real update but can simulate newer content. Use search engines with caution