How do I do that?
In the WinUAE options look for graphics adapters or Zorro 2/3 section. It can emulate graphics cards such as the Picasso - but you'd need to install the driver software like you would on a real Amiga.
To be honest I only recently updated my WinUAE from an old version 2011 or there abouts and back then I used UAEGFX which is what appeared in the list of screenmodes on Workbench as there was no Picasso or such emulation then - only UAEGFX. The special driver was included with WinUAE and it was called in the Amiga boot sequence. I think it has been that way since early 2000's. This was great though as you could have huge lighting fast 24bit Workbench and software in excess of any real Amiga Zorro card.
Now though, real Amiga graphics cards can be emulated too and I'm assuming you'll need to download real Amiga drivers for them. My UAEGFX doesn't work now after the update, which I need to look into at some point. LOL
This might help:
http://eab.abime.net/showthread.php?t=84782
