Hate to disagree with Jim on this but in all my years (40 or so) of driving I have never experienced a leak due to changing oils of any kind.
The theory sounds good but, with today's seals, I have not heard this theory advanced at all.
Having said all that, I would simply switch to M1 0W-40 and stick with that. It is a very high quality oil. I would also change the filter, of course.
Now, as to how often to change, well ..............