You'll need a bearing press to replace them - might be a job for your LBS if you don't want to invest in the tools yourself. Won't be too expensive though it's a 10 minute job.By the looks of it they have the model number on the hub in big lettering so you should be able to find replacement bearings without too much trouble. Then it's a case of finding an appropriate vid on YouTube to show you how to remove and replace them.