Remove the pieces of vinyl siding from around the window area.
Cutting siding away to remove an exterior windows.
Measure the length of the section of wall you re covering with siding.
Use a siding removal tool.
Slip the curved end of a vinyl siding zip tool into the seam between two horizontally interlocking runs of siding that you need to remove.
The total you get is how much you ll need to cut off the siding.
Then subtract that amount from the length of the piece of siding you re going to cut.
Remove all the trim from the wall having the siding replaced.
Caulk the new one in using some good urethane sealant and hope that it never fails and that water never gets behind the siding at any point above the window.
If you re intent on disregarding standard installation procedures then use a reciprocating saw to carefully cut around the edge of the window in order to get it out.
You can also cut the siding back far enough to reach the flange and then install new trim around the new window.
Work the pry bar along the entire length of trim.
Extract nails keeping the vinyl pieces in place in order to prepare vinyl pieces to be removed.
Use measuring tape to measure how much siding you need to cut off.
Wedge the pry bar under the trim.
Do not cut the vinyl off.
Use this tool by inserting it where a piece of vinyl overlaps a piece below it and then sliding it across until you reach the end of the piece.