Suitable graphics card for Lenovo H30-00 microtower?

I want to upgrade my graphics card in order to be able to accommodate gaming, however as my PC is a microtower the choices are limited. I would really appreciate it if you could suggest some options (something powerful e.g. To be able to run The Witcher 3: Wild Hunt etc) I have a Lenovo H30-00 with 8gb RAM, 500 GB hard drive, Intel HD intergrated graphics.

I know I will probably have to upgrade my PSU too.

That model seems to have an external PSU, like a laptop adapter. You can't power any significant video card with that setup. Also, even if it has a standard power plug, you can't upgrade the PSU, those small form factor cases all have custom made PSU.

Basically, you have a laptop style motherboard inside a box, not really that upgradable at all.