[c00p3r]

I thing you should start a hiring process and make it visible and obvious to everyone. Start interviewing young guys and make it clear, that you will replace anyone when you will find a better performer.

Make it clear that you want to establish a competition, and reward only the best performers. Consider a football team as a model.

Then replace just one worst guy with a young and ambitious geek - it will be a bold and clear message to rest of your team.