Use the aptly-named F12 tools (yes, you press F12) and you can switch to a different rendering mode. Note that the emulation is a close approximation and is not perfect. Actually in IE11 it's not even a close approximation (which is unfortunate because the F12 tools are much better than all previous versions), so stick with IE10 if you really need to emulate older browsers. You could also use a virtual machine and install an older version of Windows and use a real instance of IE8 and 9.
Ok, I guess that I am confused. I just need it for one application. So, should I downgrade to 10 and emulate or get a virtual machine? I've decided to go with a Virtual Machine. Thank you!