To remove your machine:

Release the tension on the rear roller. Slide the machine down to one end of the frame. Remove the roller and pull it through the throat of the machine. If your machine has a smaller throat, make sure to remove the end of the roller without the ratchet wheel.
See Fig. 1a.

Set the roller on the front of the frame. See Fig. 1b

You should be able to lift the machine off the carriage. You may want to place a heavy book on the carriage to prevent it from tipping over.
See Fig. 1c.

Fig 1a. Release tension and pull roller thru machine throat.

Fig 1b. Set roller aside.

Fig. 1c. Remove machine, put book on carriage to prevent tipping.