In general most replacement windows will include step by step instructions on how to replace. Depending on the location of the window the job could be easier or dangerous. The most important part of the job is correctly measuring the old window. If you measure correctly the new window should pop right into place however if you do not meaasure correctly the job might prove impossible. When you install the new window make sure that it is level and plumb to avoid any leakage issues. Also make sure you secure the new window to the frame using good quality screws of the proper length and size and be sure to use proper caulking to seal the window frame