Here is a short tutorial on how to hex achievements manually made By Me (OmegaModz) there is no pics because i do not think that they are needed.

1) well, to start with you will need a hex editor and your profile.
2) Drag your profile into the hex editor or open it.
3) Then search for the achievement you want to hex.
4) Make sure you tick the "unincode string" checkbox when searching.
5) After finding the achievement you want to hex go to xbox.com and see how much the achievement value is for that achievement.
6) Then open up a standard windows calculator and go to scientific mode.
search the value of the achievement and convert it from Decimal (Normal number) To Hex.
E.g if the achievement is worth 5 in decimal it will be worth 5 in hex too.
7) Then search for the Hex number in the line the achievement name is (it will be a few characters before)
Then look back 2 spaces from the achievement value and replace "00" with "12".
9) The Achievement will now be unlocked.
10) Save, Rehash and put back on xbox using xplorer, easy