Since last time I used BitTorrent to download some movies, the APP cause me some trouble such as junk advertisements, always ask me to download another APP,I didn't know how to uninstall APP until now.so here are some way I found on the internet.
Application Bundles
If you control-click (or right-click) on an Application icon, and you see "Show Package Contents", then it is a bundle,you only have to drag them to the Trash.
Additional Files
To remove an application's icon from the dock make sure that the program is not running at the time, then simply drag the icon off of the dock and let go. There will be a puff of smoke animation and the icon will be gone. This will only remove the dock icon/shortcut, and will not touch the application itself or any of its support files.
Using Finder to remove Application Bundles and Additional Files
more complex way
Launch Activity Monitor and change "My Processes" at the top to "All Processes", then make sure the app you want to remove is not running. If it is, quit the process before proceeding.
Launch Finder and search for the app name (hopefully unique, such as Skype)
You can narrow the search to specific folders or search your whole Mac
Searching "File Name" vs "Contents" usually provides better results.
Click the + button below the search term to add criteria
Click the search criteria drop-down and select "Other...", then "System files"
Click the "don't include" and change to "include"
Sort by name, kind, date, etc. to identify components of the app, such as folders, .plist files, cache files. etc.
Delete all files and folders related to the app.
Don't empty your Trash until you've determined that everything is working OK, in case you need to restore something you deleted by accident.
A reboot might be necessary to completely remove some apps.
Applications with Installers/Uninstallers
Check the installation CD or disk image for the original installer file. Some vendors have included simple Perl scripts that will run in the command line to uninstall applications, and may be named "uninstaller.pl".
Third Party Uninstallers
such as AppCleaner, AppTrap, AppZapper, CleanApp and TrashMe, but these apps will not remove all components of installed apps.
http://guides.macrumors.com/Uninstalling_Applications_in_Mac_OS_X