Window Replacement in the Home
Depending on the style of your old windows, there may be several methods of replacement. It can be done with a full frame replacement, which is the most thorough way to do it and will be your only option if your current windows are not the old-style double-hung wood windows. This requires removing old siding and trim to access the rough opening. However, you will not need to go so far, before you buy your new windows. To measure the rough opening you can drill a hole in the sill or the jamb and stick a wire through until it stops. Add these measurements to the dimensions of the existing window will give you the dimensions of the rough opening.
It is usually wise to have your new glass windows at hand before removing the old ones. To remove an old window remove any exterior frame and siding near the window. If you are planning on reusing any of these materials be very careful in the removal process. To remove interior trim, be sure to score around the trim board with a utility knife so that you do not remove paint and plaster from the wall when you remove the board with a pry bar.
If the old window you are removing is an old wood frame glass window, it is probably secured by nails going through the head, sill and jamb and into the rough frame. You can cut these fasteners using a reciprocating saw. Be sure to have the window secured so that it does not simply fall when all the fasteners are cut. Other style windows will have to be pried out of place by removing the roofing nails securing it.
When you have removed the old window check for rotten wood or weak nails and replace where necessary. Now install the replacement window the same way you would install a window in a new structure.
But there are other types of replacement windows. You can buy double-hung windows that are called "replacement inserts". To put these in place is a relatively simple process. Using a small pry bar and a putty knife remove the interior stops on your old wood-frame window. (Here again you want to score the seam between the stop and the old window frame to avoid paint flaking, etc. Remove all finishing nails that might be poking out.
Make sure the replacement insert is close to the right size by pushing it into the opening from the INSIDE of the house. (You might want to have someone on the outside to help prevent the window from going all the way through for any reason. As you can imagine, you need to be somewhat precise regarding the fit. Replacement inserts are usually adjustable, but only to a point. Put a bead of caulk along the inside of the blind stop, then re-insert the insert. Secure it in place by screwing it partly into the old window jamb in the places indicated on the insert.
Now check for level and test that the sashes open and close properly. Shim as necessary and then finish screwing in the screws. Now replace the interior stops and trim the window as appropriate. You may not have to trim at all!
A more complicated procedure involves purchasing double-hung sash kits. This is more labor intensive and requires much more precision. A kit will come with its own instructions that vary depending on the manufacturer. However, the gist of it is that you will be removing the stops, mounting tracks on the old jambs, replacing the old stops and then inserting the new sashes.