i live in seattle and the weather has gotten to be really chilly. anyway, i use castrol gtx 10-30 and was thinking about changing to 5-30. should i stick with
10-30 or switch over to 5-30? also, if i should switch to 5-30, do i simply drain the 10-30 and fill with 5-30? tried searching through oil change topics, but couldn't find anything. TIA.

 

According to the owner's manual, 5W30 viscosity is preferred at all temperatures. I use it year round.

Yes, you simply drain the oil and refill it with a different viscosity. Same procedure as any oil change, nothing special required when changing viscosities.