If the Oven is not heating or not heating to the correct temperature try these troubleshooting techniques 

Check to see if the element is bad:

Place oven on 350 degrees, the lower element should start to glow bright red, if it does not glow within 1 minute its time to work through other troubleshooting steps.

Let oven cool and then remove all racks to clear out working space.

Remove element by the 2 screws in the back, and pull gently to detach to reveal the connections which should be able to slide off by hand.  Be sure to pay attention to the colors/side of the connectors

Check the leads on the end, check for breakage

Use multimeter set to continuity setting.  If the meter doesn't chime/detect continuity its time to replace the element

Check out the video below for a detailed guide and tips!