Thank youHomeSealed said:First, if you have trim around your existing windows, only that will need to be removed in most cases, no siding. Secondly, even if the siding comes directly against the existing window (meaning that the nailing flange is behind it) there are two methods: 1) Cut the siding back and then add trim over the new nailing flange (no siding removal necessary). This is fairly common. 2) Remove the siding around every window in order to remove and reinstall the new window. This is far less common unless you are replacing siding, as the majority of the siding on the home will need to be removed if you are replacing all of the windows. There are third and fourth options in an "express install" (Nail fin on existing window is cut, new window has no fin, retrofit a drip cap), and a "frame jump" (depending on the orientation of the existing aluminum frames). Those two options are less desirable however as they offer fewer layers of protection, and must be executed to a high level of detail to function and seal properly.
My advice for DIY, would be option one or two. I'd also encourage you to look up "how to" material, both videos and printed instructions so that you are able to flash every opening properly. This is absolutely critical... If you search this forum, you should actually find some links for that.