remove gears
get a simple conversion kit: tensioner, spacers, steel cog with tall teeth.
Go!
you can use a normal 32t chainring, an old one, or the one thats there already.
might as well! theyre cheap enough!
if its proper flat like, a 16t may be a bit spinny, but its a good place to start, and is normally the one that comes with the kits.
replacement sprockets are about 2 or 3 quid for a cheap pressed out one, availible in all sizes APART from 17t (for no apparent reason, they are only availible in 20 quid versions)
easiest way to check, is to go for a few rides without changing gear!
the inner ring can be removed, but you will need ether short chainring bolts or a bashring for the middlering
do it!