I don't have an '89 so maybe someone can be more specific...
Generally the injectors are held in place by the fuel rail, which is bolted to the intake manofold. First, disconnect the battery so you don't have a fire. Release any pressure in the fuel system by opening a line at your filter or something. You'll want a bunch of rags to catch the fuel that spills. Unplug the injectors, unbolt the fuel rail, lift it away from the manifold. The injectors may stay in the manifold or they'll come out with the rail. Either way, take them out completely.
The seals are like little O-rings at both ends of each injector. Get new ones all around. Don't get them at the hardware store because they have to be compatible with gasoline and the temperature. The old ones will probably be hard & brittle. Then put it all back together.