1998 Ford Windstar how to change plugs

Hello, I just bought this van from my parents. They bought the van new. The problem is that this van still has the original 3 plugs and wires on the back side of the moter due to the fact that they are so hard to get to. My father likes to fix things himself, but this one whipped him, like my father, I like to fix things myself also. Is there an easy way to do this task? Also I have another question about the air conditioning, when I turn the heat or air on the air may not come out the vent that I have selected, it is constantly changing from vent, floor, and defrost, I know that the vents work off of vaccume. Is my problem in the controll switch? Thank you !