while it's not hard, if you have never done it before, it can be intimidating.
these are rough instructions, but should provide direction.
1. remove everything that comes off on your door. manual windows? remove the window knob. there will also probably be screws around the door opener, and the handle that you pull to close the door. you might also have screws on the bottom, or the sides of the door card (the inside upholstered part.
Then you need to use a screwdriver and very carefully push it between the door card and the door. There will be plastic type screws holding the door on. They may or may not break and are avail at your local pep boys/ napa / autozone under the "help" section. start from the bottom of the door and slowly work your way up. When it's free it should lift up and let you separate it from the car. If it's caught up on something do not use force.
Now you exposed your speaker. Chances are it will use a Ford type fitting, so you will need to cut and crimp (I prefer soldier and heat-shrink myself) the new connections that came with your new speakers. They might already be crimped to wire, then you need to connect the wires together, follow the manufacturers of the speakers directions on this point. Rule of thumb is "for the stock for speaker wired, the lighter color is positive" but I have found this to not be true 100%, so start it with that in mind.
Put the new speaker in, screw it down with the 3 or 4 screws required, and reverse the process on putting the door back together.