Bike fit / correct riding position

I know the topic's been fairly well covered on here but i can't seem to find a specific answer to my question..

I'm 6'1" and ride a 56cm bike. I know it's probably too small for me and causing the torturous pain in my knees when i ride over 40 miles on go or run over 5k.

I need to do something about it as i work for sustrans so cycling is pretty much essential for work.

Should i:

a) get clip in pedals / SPD's and pay for professional bike fit (might just end up paying for someone to tell me my bike is too small).

b) buy new bike and get professional fitting at the same time (can't really afford this option).

Any help would be greatly appreciated :)

Sam, this is far too little information to go on. What's your inseam measurement, for instance? For most people who are 6'1", I'd say definitely get rid of the current frame and get at least a 58/59cm frame.

However, I don't know you and it could have something to do with one, or several, of the contact points between you and your bike, the distance between saddle position and handlebars, etc. It's not rocket science, but there are quite a few factors.

This forum isn't necessarily the best organised for understanding basic bike fit (your question has definitely been covered before, but that's not necessarily easy to find). There are a lot of web-sites that cover it in as much depth as you want it.