What version of iOS are you running rania? Higher then iOS 5 (not sure about exact version numbers) and replacing files un-jailbroken will not work, as files are read only past that point.
Otherwise, you can use a program such as iFunBox or iExplorer* to replace the file named crosshair.png with a modified version, which SHOULD change your characters look, if not make sure you don't have any hats enabled.
* I have rather limited experience with iExplorer, so I dunno how well it works.
1.Junk-Jack-Wiki 2. The world is big, 256 blocks high and 768 across. 3. Who is John Galt? 4. Lack of objection does not indicate consent. 5. We scream, we shout, we wail, we cry; but in the end we all must die.