Defrost problem on a LG Bottom Freezer...

Question

Frost building up on the inside back wall of the freezer. The fan is now making noise as it works to spin against the frost build up. Where is the manual defrost timer switch and how can I get at the the defrost limit switch on this manual. Also is there any thing else I should be looking at? The model is a bottom freezer single top door with water dispencer and ice maker. Ihe MODEL IS LRDC 22744 ST