If you really want to change just the bearing, you need to take the wheel and castellated nut off and see if there are any markings. If I recall correctly they are all the same, but you'd ideally check.
BUT - it's often easier/similar price/safer/worth it to replace the whole hub. You'd get a pair of hubs for £40 on eBay. (You'd probably pay about £15 for two bearings)
__________________
|