How do you remove the sprocket from an eighthinch splined BMX style crankset?
Tap tap tap tap tap. 

And then tap tap some more. 

If this is what I am thinking of you either tap the inside of the chainring from the non drive side. Or you tap the spindle from the drive side which should push the spindle through the chainring and bottom bracket. Or a little of both. 

Tap tap with a wood block.

Greasing before install goes a long way to make these things easy. They are made to be tight!

You could improvise a automotive gear puller but the hammer should work.