Sorry if this question seems dumb, but when I'm checking in do I need to ask for an upgrade or will they automatically give it to me? What can I expect at a JW when I book a 1 King room?

not dumb....and you will get an array of answers....

Many people will ask nicely for an upgrade...i generally do not unless i am someplace really special...IMO if the T & Cs of the MR program call for an upgrade to the ' best available room....' then i would hope that they would follow the program. If I get a particularly lousy room then i will go back and ask for something better......

As for a JW, well you don't say which one......but for example, at the JW in DC I would expect at least a nice CL room with a view of Penna Ave (if such a thing exists..) [Incidentally some of that hotel's desk staff was rather rude to me a few weeks ago when i wanted to see a room. I had to play the DYKWIA card-which i really don't like to do-and was a little bummed to see that their rooms are well, rather dull....YMMV. Stayed at the Mayflower instead and wound up with a nice, albeit in need of some TLC, suite...]

If available, you should be upgraded automatically. Ask questions here on Flyertalk to learn about your hotel now. Then prior to arrival call Marriott and make a request - like "corner room facing the courtyard".

You should at least get concierge level or concierge level access.

I also rarely ever ask for an upgrade at check-in but in the last few years I have experienced it all: upgrades to suites or larger/nicer rooms. Sometime you get a room in the same category as booked but in a nicer/quieter part of the hotel. Many times I also get a room on the executive floor* (where you might have some extra perks such as free minibar) and just last week I was offered one of the first freshly renovated rooms at the Renaissance in Brussels.

* Of course as a gold/plat you will always receive access to the executive lounge, at least I was never denied access.

thanks everyone! I'm going to be at the Houston JW this week. I saw the thread on Houston Marriott's and someone got a plat upgrade to a 1200 sqft suite! I'm tempted to ask if room 349 is available just to see the look on their face when I check in. I'm happy with the club level though, so hopefully they'll have rooms.

I find, at the PLT level, if you don't ask (via several avenues as noted above), you generally will not receive, even to something as simple as the Club level. YMMV.