How can I uninstall a plugin?

If using Mac OSX: look into your library under:

/Library/Audio/Plugin-Ins/VST for the VST version
and
/Library/Audio/Plugin-Ins/Components for the AU version

Delete all files that start with [name_of_the_plugin].[whatever_extension]
Also look in this path:

/Library/Audio/Presets/GSi

Delete the folder [name_of_the_plugin], and if you don't have any other GSi plugins installed you can also delete the upper folder "GSi".

Pay attention: Mac OSX has two libraries, one is the System Library under MacintoshHD and the other one is the user library under [name_of_your_user]. According to how the plugin was installed, the files may be in the system or in the user library, so make sure you've looked into both lbraries.

If you're using Windows, instead, the thing is way easier: go to your VSTPlugins folder and delete all files and folders that have the name of the plugin. The VSTPlugins folder could be:

C:\Program Files\Steinberg\VSTPlugins

The folder "Program Files" could be translated into your language, so for example for the italian version of Windows we have "C:\Programmi\..."