CAUTION USE AT YOU'R OWN RISK! I AM NO PROFESSIONAL, THIS IS JUST WHAT I DID TO MAKE THE JOB A LITTLE EASIER.
I have recently done this on a 1990 subaru legacy 2.2l. It is fairly easy but, caution should be taken because if you don't relieve the fuel system pressure properly you will have lots of problems. the reason i changed the fuel injector was because the engine was getting bad mileage and was loping. first thing is to make sure you need an injector, i am not an expert and i didn't know how to read the codes so i had to use a process of trial and error. Once you know that your injector needs replacing the first thing to do is to relieve the fuel pressure. that can be tricky because on this particular model the only way is to unplug the fuel pump and and turn over the engine for at least ten seconds, i did it for twenty just to make sure. if you are reading the manual they say to pull the fuel rail. i didn't it made the job way easier what i did is first i took loose one of the fuel lines to the rail to ensure that there was no fuel in the lines THIS IS IMPORTANT. if you don't do that than when you pull the injector and if there is still fuel in the lines it will fill up you'r intake you don't want that to happen. once you have pulled the fuel line off (make sure you don't loose the o-ring) you can unplug the injector and remove the top piece that holds the injector in. Now you can firmly grasp the injector and pull it out twist as you pull and it will help. it will be hard to get out so you will have to pull hard i used a pair of pliers (don't do this if you plan on putting the injector back in it will damage it). now if you are planning on putting a new injector in you need to oil the o-rings (USE CLEAN OIL!) and push the injector in as far as you can then put the top piece back in and screw down till snug, plug back in, connect the fuel line back up and plug in the fuel pump. if you are replacing more than one mark your wires! If you are putting in you old one back in put new o-rings on it and follow directions for putting in new injector.