OS: Windows 7 64-bit
While this may seem like a simple task and should be obvious, it isn't.
For whatever reason, my instance of Trillian didn't create an entry in Add/Remove Programs, nor an option in the Start Menu.
Using the following run line I was able to uninstall the software:
"C:\Program Files (x86)\Trillian\trillian.exe" /uninstall
Note: Check the location of your installation and modify where necessary.