Remove the old window. If you are working with a large window, you will need someone to help you. To remove the window, you will want to carefully remove the vinyl siding from around the window, remove the old J Channel and trimmer pieces and remove the nails holding the window in place. Set the old window aside.
Strip the interior of the window opening. This will include removing about a six inch perimeter of dry wall around your window opening, removing the window sill and removing the old window trim.
Prep the new window frame for your Speedset glass block windows. To do this, you will want to mark the location of your accent block windows, which will usually be four inches to each side of the main window opening. You will also want to create plumb lines and vertical lines for your block windows using a level and your pencil. The plumb lines will be set about six inches apart, as will the vertical lines. When you are done you will have six inch blocks laid out.
Install moisture barriers before installing your glass blocks. Once installed, you will be able to nail down the bottom window jam piece. Next you will apply a thin layer of mortar to the window opening and your first row of glass blocks. Use your level to ensure the blocks are level. Apply a small dollop of mortar between each block to hold them together. Use a damp cloth to wipe away any excess mortar as you progress. Continue until you have finished installing all of your blocks.
Apply expanding foam insulation between the glass blocks and the window jam. This will help keep out drafts. Once this has set up you will want to trim out your window.
Repair the interior and exteriors of your bathroom wall. Inside, you will want to replace the window sill, dry wall and interior decorative window frame, and on the outside, you will want to replace the moisture barrier and vinyl siding and exterior window trim.