There are two temperature sensors (one in the refrigerator and one in the freezer). The refrigerator sensor is near the front of the compartment on the right side below the door switch and above the slides for the drawers. The freezer's refrigerator temperature sensor is on the left near the top of the compartment. See the two liner diagrams on the page linked below. To change the temperature, press and hold the Temperature button on the LCD panel for 3 seconds. The display should read the current temperature set point and Refrigerator. Use the Acceler-Ice button to lower the temperature in the fridge. Press the Lock button to raise the temperature in the refrigerator compartment. Press Temperature again to see the Freezer set-point and adjust it as above. Note: the temperature in each part of the unit depends on air circulating from the freezer into the refrigerator. Make sure that the vents aren't blocked. Wait 24 hours after adjusting the temperature set points for the unit to reach equilibrium before deciding if the set point should be adjusted further.
Sears Parts Direct has the parts diagrams for the 106.51139210 here: https://www.searspartsdirect.com/model/4lfq9qfxpx-000582/kenmore-10651139210-side-by-side-refrigerator-parts
. This page also has a link to the owner's manual for the side-by-side refrigerator, https://c.searspartsdirect.com/mmh/pd_download/lis_pdf/OWNM/1302214L.pdf
. See page 15 of the manual for the information on setting the temperature set-points.
I hope this helps.