The pitch bend range for each layer is found in Misc Parameters (the button under the display). It can be set independently for each layer, so you'd simply set the value to zero to disable it on a given layer. The mod wheel can also be disabled for each layer independently within the Modulation section. Press "source", use the select knob to find the mod wheel routing you wish to disable, and set the value to zero or the destination to "off".
You're probably already aware, but because you mentioned you're new at this, you toggle between editing of the two layers with the Edit Layer B button.