Disconnect the negative battery cable from the battery.
Disconnect the 1995 Volvo 850's air intake ductwork by removing the clips and snapping the ductwork out of position. Unscrew the engine cooling fan shroud, which is held in place by four screws along the top side of the radiator. Also unclip the electrical tab that connects the fan with the engine's electrical harness. Doing this will reveal the starter and give you room to work. If you are unsure of what the starter looks like, it is in the shape of two cylindrical pieces connected together, with one piece noticeably bigger in size.
Unbolt the two screws that attach the starter to the engine block, using the socket wrench. Place the screws in a place where you will not misplace them. Unclip the electrical connection from the engine to the starter by hand. There is a screw at the end of the starter opposite the longer screws that you first removed; unbolt this screw in order to remove the starter from the mounting bracket.
Put your new starter in the same position the old one was. Screw in the mounting screw first, then the two bolts on the front side of the starter. Then reattach the electrical connection.
Reconnect the negative battery cable and start your Volvo. Don't put all of the pieces that you took off back together again. This is so you can test the new starter to make sure you have aligned it properly with the flywheel and the Volvo starts up right. If it starts up, reconnect all of the rest of the parts that you took off in previous steps.