If you have a two story house and you are going to replace the windows on both the first and second floor, there are little tricks that you can use to make the upper floor job a bit safer and easier. If the windows are replacement style frames, you install them from inside the house, so the only thing that you will do different than the first floor windows is to use an extension ladder to caulk the exterior. So, let's talk about doing retrofit style windows on the second floor. You can usually remove the old window from inside the house, but if you have a picture window, you have to use the extension ladder to remove the stops holding the glass in place. Then, you can go inside the house and cut the glass free from the frame using a utility knife. Put a tarp on the ground below the window, to catch any glass pieces that may fall during the removal. Also, don't forget to keep people and animals away from the area below the window.
Once you are ready to install the new window, you can do it from inside the house. Remember, when installing retrofit style frames, you install them from outside and raise them into place. Instead, carry the window upstairs. If it's a slider, remove the screen and sliding panel. Then, using a helper, you can angle the window frame through the opening, extending the retrofit lip completely outside of the opening before pulling the window back toward you, and installing the window as if you were outside. Have your helper hold the center bar while you put a screw into the top center to hold the frame in place. You can do the entire installation from inside. The only time you will need to go on the extension ladder is when you're ready to caulk the exterior. Make sure you put a generous amount of caulk where the top of the frame meets the stucco or exterior material. You don't want any water getting past the new frame, otherwise it can work it's way through the wall and down through the ceiling or the walls.
You would be surprised how easily two people can install an 8' wide by 5' tall sliding window on the second floor if you remove the sliding panels and screens. In fact, my helper and I did one 10' wide and 5' high. That was the biggest one I ever did on the second floor. You can run a bead of caulk on the outside face of the old frame before installing the new frame right from inside the room.
Now, if you are installing a picture window, it's a little tougher. You can't remove any panels to lighten the load, and it's tougher to get as firm a grip on the frame. But, on the positive side, picture windows aren't usually much larger than 3' by 5' on the second floor. If you have a large picture window, or if you have several to install, I have access to suction cups that are used in the glass industry. You can attach them to the glass and use them as handles when extending the frame outside through the opening. Contact me on my website at How to install windows if you want to get pricing on suction cups. You can get the smaller, inexpensive models for around $40 each.
So, if you are hesitating to replace your old windows yourself because you didn't think you could do the upstairs windows, now you know you can.