Ok I have never done the fuel injectors on an Import and sometimes they can be very different then a domestic car so keep that in mind.
An example of this are nissan fuel injectors. Most of them are bolted into the fuel rail and are actually part of the rail unlike most other designs that just clip onto the rail.
If you could get a picture of the injectors that would be great. I will tell you want I have learned based on the cars I have done though.
I would advise spraying the top of the engine down with compressed air or something to blow any debris away from the injectors. You do'nt want any dirt falling down the holes when you pull them out.
You don't need to turn off the fuel pump or anything like that. What you do need to do is first pop the gas cap to reduce the pressure some and then find the little schrader valve that is on the fuel rail somewhere. It will probably be covered by a cap that looks just like a tire stem air cap. There is a special tool that can be used to relive the fuel pressure but you don't need that. Just make sure the engine is cool and place some rags under the valve then press on the valve with the back of a tire pressure guage or something. Some fuel will squirt out and after a second or two the pressure will drop off.
Now assuming these injectors are like most domestic and some import style they will be held in by little metal or plastic clips. A small flat head screwdrive should be able to pop them off. Try not to lose them but if you do it is not that big of a deal because once the rail is fuel rail is bolted down the injectors are not going anywhere.
Once you have all the clips removed from the injectors go through and mark all the wires leading to the injectors. This way you won't get confused and hook the wrong wire to an injector. Now you need to unbolt the fuel rail from whatever it is attached to. There will probably be a few bolts holding it to the intake. Just remove all of these and set them to the side.
Now you need to look at the fuel line and return lines that go to the fuel rail. On some cars you might have to disconnect them in order to move the rail enough to get the injectors out. On a subaru I have no clue how much room you will have to just look at them and eye ball it. You might want to go to your local library and see if they have a chilton or haynes manual for that particular model. Most of them will and you can just xerox copy the section you need.
Once you have that figured out you just need to give the rail a good tug to pull the injectors out of the intake. Try to pull it evenly on all sides since most rails are out of aluminium and they can be bent easily.
You will probably have to tug and wiggle at the rail for a while and some of the injectors will pull out of the intake and some will pull out of the rail. Once you have enough room to pull the injectors all the way out do so.
Ok once you have all the injectors out set them aside and get your new ones. Look over them carefully to make sure all of the look ok. Pay special attention to the O-Rings on them to make sure they are good and don't have any scratches, gaps or cuts. I had a couple of injectors one time that had damaged O-rings and it sucked.
You will want to put a little light oil on the injector O-Rings to help them slide into place. Since I work at a shop and we have thousands of gallons of motor oil around I just rubbed a little 10w 30 on the rings to lube them up.
I found it easier to slide all of the injectors into the rail first and then push the rail down so till the injectors locked into the intake. This will probably take a lot of wiggling, pushing and cursing but just be patient and keep even pressure on the rail.
The rest is just the reverse of removing all the parts. Just hook everything back up give a good double check all the fuel lines are hooked up if you removed them and have one person watch the motor while the other person mans the ignition. Turn the key to on first to let the pressurize prime the system and that will help you check for leaks. Any large leaks will show up when you prime the fuel system.
Then just crank the car till it starts. It will probably take a lot of cranking because the fuel system will still be low in pressure and partialy empty but the car should start eventually unless you really screwed up some where