Hi Dorothy,
You don't! First you have to free the carriage.
The first thing to do is remove the yarn from the feeder, then loosen the thumb screws on the sinker plate assembly and ease it away from the carriage, lifting slightly as you pull it forward. Unlock the carriage using the change knob/lever and lift it away from the needlebed.
You should now be able to move the needles forward to check them. Push back those that are OK to non working position, leaving the damaged ones forward. Now remove the sponge bar and replace the damaged needles, closing the latches to remove them and opening the latches on the new ones before replacing them. When you replace the sponge bar, hold the needles down with the flat edge of the needle selector so that the sponge bar goes over the needles. Check that the sponge bar has at least 1/4 inch of foam above the metal all the way along it and get a new one if the foam has compressed.
Don't try to remove the sponge bar whilst the carriage is jammed as the needles will be loose and cause more problems.
Sue, June 2011
