How can I upgrade the wiring in my home?

Yes, buy them at the store, shut off power, unwire the old ones and rewire in the new ones.

I did this in my parents home several years ago. The electrical boxes must be metal. You will need #14 green insulated wire for a ground. Take a short length, about three inches, of wire, screw one end into the back of the box and the other end to the ground connection on the outlet. Connect the black and white wire to the proper screws on the outlet.

Not sure...ask an electrician.....meanwhile I use the adapters when needed.

Your three prong plugs will not be grounded unless you have a ground wire that runs all the way back to your electrical panel. You can install a gfci outlet, which will protect you from a shock, but will not protect what is plugged into it. Grounding from the outlet to the metal box is dangerous as the box can become live and potentially start a fire if it overheats. Installing a three prong plug may lead someone to believe the outlet is grounded when it is really not. At least use a gfci if you do not want to rewire. NEC code does not require you to rewire what is already existing, but you do need to use a gfci outlet.

Unless you have been trained in electric wiring, you should pay a bonded person to do the work for you. This is not something you want to do by trial and error. Wiring a home is dangerous working and later for fear of fire. I strongly advise you to have a qualified person show you and work with your or hire them to do it.

I noticed that the GFCI outlets as mentioned by Seth to replace older 2 prong outlets sometimes have a notice on them indicating they are not grounded.