Jump bike gearing question

othello

I picked up a second hand jump bike for my son, and I want to change the gearing, but I'm a bit stuck as to the options. We've not owned a single speed jump bike like this before (lots of MTBs over the years just nothing like this).

Current set-up is as the pictures. Single speed and looks to be a 28x15 gear set-up. My son wants a lower (easier) gear, so I'm looking at adding a bigger rear cog, as I assume that will be simpler/cheaper.

* How does the freewheel come off (i.e. what tool do I need) and do I need to look for a specific type as a replacement?
* What pitch is the chain/cog usually, as I expect I'll need to add an extra link or two which I might have in my spares box.
* Anything else I need to know?

The Rookie

The rear cog screws on like a freewheel, unscrew and fit a bigger one, chain is normal 1/2" pitch and either a fatter 1/8" single speed chain of a 5/6/7/8 speed 3/32 chain.

othello

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19744269#p19744269]The Rookie[/url] wrote:

The rear cog screws on like a freewheel, unscrew and fit a bigger one, chain is normal 1/2" pitch and either a fatter 1/8" single speed chain of a 5/6/7/8 speed 3/32 chain.

OK, so I'm just looking for a screw on freewheel. Any makes I should be looking at?

The Rookie

Perfectly useable
http://www.planetx.co.uk/i/q/SKSP18FW/sprint-s-s-1-8-freewheel