Premeasure & Purchase

• Measure the rough window opening. To obtain a precise measurement you will need to remove the interior trim from around the existing window. Measure the height and width of the opening between the framing members: header to sill and side cripple to side cripple. Purchase a vinyl garden window that will fit within the existing framing.
  
  

Remove the Old Window

• Remove the old window from the exterior side of the window. Remove trim boards around the window carefully, so you can reuse them if applicable. Pull the nails holding the window frame in place. Inspect the framing members once the window is removed. Check for level top and bottom, and plumb the sides. Remove any interior trim and screws or nails that remain inside the window opening.
  
  

Preparation

• Dry-fit the new window by putting it in the opening and testing the fit. Remove the window and correct any framing defects to improve the window's fit as needed. Install tape metal flashing around the exterior of the window opening, and on the interior side of the upper corners of the window frame.
  
  

Installation

• Put the new window in place, check for level on all sides and fasten by nailing through the nail fins of the window. Use galvanized 8d nails for window installation. Replace the trim around the window, and caulk between the window frame and the trim boards.
  
  

Considerations

• Consider carefully when choosing your window; there are a number of options, price points, styles and manufacturer warranties to choose from, and decide who will install the window. Determine the quality of the window by the quality of the manufacturer's warranty. You will pay more money for a higher quality window, but you should never have to replace it, either.