Simple... I'll tell you how I would do mine... you may have to adapt if you have a split tank.
First follow this thread.
http://www.bigdogbiker.com/forums/how/451-how-remove-install-swap-your-speedo.html
When you get to the point of it being apart...
Then with it apart, pull the tach wire harness pictured here
Pull the 2 nuts removing the bracket assembly.
Then the speedo will slide thru the front.
Then pull the catch ring holding the tach in. Slide the board out, minding the LEDs.
Don't think you will need to pull the foam... but here's all the parts for that.