You can check by pulling the valve cover and looking at the rack and plungers that slide in and out of each individual injector. They should all be in the same position relative to each other. In other words if one is all the way in all of them should be the same, and if all are out all of them should be out.
If I'm understanding right, in your case you say the problem seems to start when it gets hot so you might need to run the engine to get it hot and then shut it down and pull the valve cover. In most cases you can then restart the engine and watch the rack when you hit the shut down lever. It might spatter a little oil around with the cover off, but as long as you don't rev it up it usually won't make a mess. If all of the injectors don't go to the no fuel position when you hit the shutdown, then a stuck injector is your problem.
If that is your problem you can change that one injector, but I really wouldn't recommend it. Usually changing just one puts more load on that one cylinder than the others due to the injector being clean, etc, and that's not really a good thing. To change them isn't that difficult as long as you have the info needed to do the job. There is one special tool/guage that is nice to have, but it can be replace with a depth mike or a good set of calipers with the depth guage feature if you can't get your hands on the tool.
Ultimatly you need a bare minimum of a manual for the engine to do much of anything. If you don't feel like it's something you can handle then by all means call someone that knows what they are doing because the injectors have to be timed to each other (with the rack) properly, and timed for stroke (with the special guage) or the engine will not run properly. Too, it would be a good thing to have someone basically make sure all of the governor adjustments, etc are all good too, in other words give it a tune up. So, really, if you have to replace any injectors, etc, getting someone that knows the engines and has the tools probably wouldn't be a bad idea anyway.
Good luck and if you have any more questions feel free to ask. Wayne