I need to reinstall Itunes but I can't find Itunes in my system to do so, Help please?

So recently my computer has been having some trouble and I have found what was causing it and put a stop to it, but now apparently I need to update my itunes, but to do so I need to reinstall Itunes, but before that I can do that, I need to change my path to my Itunes which I can't find anywhere. So I got reading a question similar to this and saw that I should install msicuu2.exe version 3, so I tried but because my system likes to play up it states that it can effect my system and block it out, leaving me with nothing else. I have done everything I can to fix everything defrag ectra even my wizz tec friend can't find itunes. So does anyone know what I can do? I'm a person who can't exsactly with music or my books which are on there. I would Put them on my Phone but my memorys full with documents from my writing. Please please help me out.