There's no point in major upgrades until you've had plenty of time on the bike to learn what works for you and what doesn't. The bike is a decent starter for a beginner. Read the forums and magazines to increase your knowledge, but most importantly, ride the bike regularly, without overdoing things until you have built up your fitness.
There's good advice already on tyres, pedals, shoes and pumps and maybe a saddle. There's no point buying major items like wheels and spending money without really knowing what you're trying to achieve. If you have money to spend, best to get some decent cycling clothes, tools and spare tubes etc., so that you are comfortable on the road and can deal with any problems you might encounter.
There's good advice already on tyres, pedals, shoes and pumps and maybe a saddle. There's no point buying major items like wheels and spending money without really knowing what you're trying to achieve. If you have money to spend, best to get some decent cycling clothes, tools and spare tubes etc., so that you are comfortable on the road and can deal with any problems you might encounter.