itunes help: How can I remove an old copy of QuickTime that won’t uninstall and won’t allow me to install or use ITunes? - Help.com

when you say won’t uninstall, what do you mean? (e.g. what error message/s is it bringing up, how far is getting before crashing?)

Hello,
Presuming that you have a Windows Operating System, It is probably because a process is running preventing you from doing so, my reccomendation is to do the following:

1. Shut-down computer - or restart either will work, once the BIOS screen pops up on loading you will be fine (the BIOS should always appear when loading).

2. Turn it back on, and press F8 (most common button - may change on other computers) to get up troubleshooting screen.

3. Option 1 is safe mode, option 2 is safe mode with networking and option 3 is safe mode with command prompt, ither option 1 or 2 will do you just fine.

Once Windows boots up in safe mode, do the following:

4. Control Panel - this is the area where you can change many settings

5. Programs and Features (VISTA) or Add/Remove programs (prior to Vista) this is where you can uninstall and/or install software or Windows features.

6. Uninstall Quicktime

Once done do the following:

7. Reboot and start windows normally

8. Install iTunes.