A Roman blind is composed of a single piece of fabric that has a cord attached to lift it up or down. You may need to shorten the blind if you've measured improperly or if you want to move it to a window that is a different size. You can probably do this yourself with a few tools.
Determine the length of the window using a metal measuring tape. Metal is a good choice because it does not stretch like other tape measures do. Record the measurements with a pencil and piece of paper.
Completely extend the blind with the lift cord. Lift the blind out of the brackets above the window and lay it flat on a large surface such as a table. Untie the cords from the bottom rings on the back of the blind.
Mark the blind with a fabric pen at the length you wish it to be by using the window measurements. Add an additional 4 inches to account for hems. Draw a straight line across the blind with a measuring tape to keep the line straight. There should be two lines, one for the exact length and one for the hems.
Cut across the hem line with scissors, making sure to keep the line straight.
Fold up the fabric until it reaches the length line. Secure the fabric in the back with a hot glue gun, which will create a hem for the blind.
Reattach the cords to the rings on the back side of the blind.
You can use a clear adhesive or wood glue if you do not own a glue gun. Add a few additional stitches for extra support at the hem if you feel it is necessary.