How difficult is it to replace windows in my house?

Window replacement in itself is not too difficult a process, although there are legitimate reasons for hiring a professional installer. As a homeowner, you can buy replacement kits, or inserts that fit into the existing window opening without the need to remove casing, trim or siding, or buy new windows that will require some remodeling.  

Either way, the job can be done by yourself but is not for everybody. Some skill and experience with power and hand tools, framing and remodeling is necessary. A poorly installed window will counteract any energy efficiency upgrades and could lead to leaks and more serious problems, like water damage and wood rot. Professional installers also guarantee their work, whereas any issue with your own work is your own problem. Safety is another concern. Hard to reach windows and large windows can be dangerous. A professional comes with a crew of experienced installers used to working on ladders and with heavy, awkward objects.  

There are resources available explaining how to replace windows in your home that could be a big help to DIY'ers looking to learn perform window replacement. However, do not underestimate the importance of safety and quality in any project. That goes especially for windows and doors, which are the most important part of a building's skin and have the largest impact on a home's efficiency.