Injector replacement is fairly easy, and there is satisfaction in doing it yourself. Do a search on "Installing Injectors" and you will be sure to find someone who has done a step by step write up.
If you have suspicion of a leaking injector, a quick and easy test for contamination in the oil is to take a cheap fast food napkin and place a drop of engine oil off the dipstick (warm/running). You will see a "not so dark" ring around the drop spread out/soak into the napkin faster than the rest. That would be fuel.
Not necessarily a leaking injector can be the cause. Bad O-ring on an injector, cross over tube are other places that can cause fuel to get mixed into the oil.