Removing Programmes

[modeller]

I want to remove various programes but I get the window say it's sharing files which are being used by other programmes or maybe needed . What can I do ?

I also have several Apple files/which I have never used or am aware of installing. Can they be uninstalled ?

[Noth43]

If it's windows, keep pressing f8 during the boot process and select safe mode.
I use http://www.piriform.com/ccleaner/download/standard and have had no issues at all, it's very good. Click options and then tools. Brillliant.

[chrisgel]

Please be very careful what and how you remove anything.