Haven't stay in a Marriott for several years and definitely before their latest website refresh.

I'm booked on a corporate rate in a 2 Queen room. A 1K on my corporate rate just become available (if I make a new booking). Is this possible to modify my reservation to the 1K online?

When I modify room type in my reservation, it will show the 1K but at public rates. If I try to change dates, it allows me to specify my corporate rate code but keeps me in my current room type.

I can't cancel current reservation and book new one as I'm inside the cancellation window.

Thanks.