Modify Executable in Windows

1. Download Hex Editor: HxD
http://download.cnet.com/HxD-Hex-Editor/3000-2352_4-10891068.html

2. Open the Executable by using HxD

3. Go the executable place you want to modify
For example (nasm format) :
66 BA 2F 05 : mov dx, 0x52f
66 EE : out dx, al