Page 16 of your owner's manual shows how to remove the drive cover on the front of the mower deck. Here is a link for your owner's manual in case you need it:
. Remove the cover on the drive belt. Remove the cable from the drive lever on the handle as shown in the top photograph in the image below. Your mower may look slightly different than the one shown below but the basic procedure will be the same. Remove the cable connection on the bottom of the gear case as shown in the second photograph. Remove the cable clip that secures the cable to the front of the mower deck as shown in the third photograph. You can then remove the cable tie(s) and clip that secures the cable to the handle. Install the new cable in the reverse order as described above.
If you do not feel confident repairing this problem yourself, then you can have it repaired by a Sears technician. Here is a link that will provide the nearest drop-off locations:
Sears Home Services