Post a to scale drawing of the spaces you want to change . This looks like a main floor master where wre the other bedrooms.? I need to see the bathroom that exists and how difficult is access to the plumbing from below? To scale on graph paer showing every window doorway , toliet position and all measurements clearly marked. Post that drawing in a comment here do not start another post Use jpeg format

I want to change the bedroom labeled "master" and the one labeled "back left" - merge them together for a master BR along with a walk in closet and a master bath that is larger than the current bath in the master. We have a full bed/bath in our finished downstairs so I am not worried about this for resale (we are empty nesters).

The new bathroom will contain what other than the toilet? Double sinks? Linen closet? Separate tub and separate shower?

new bathroom needs a larger shower, double sinks, and no tub. No need for a linen closet unless there is a nook somewhere that makes sense. Walk in closet (or bath) needs space for a stackable w/d. we have a full size in our finished basement but I'd like convenience of one floor living. We don't feel like we need that much 'space' for our bedroom -- king bed, small chair and a dresser -- everything else can be in the master walkin closet if that makes sense. At the moment, the back left bedroom is function as my walk in closet with a vanity, shoe rack, dresser, etc. my husband uses the closet in the master. we're used to separate closets but i guess i don't mind sharing... :)

Thanks @thinkdesignlive for pointing out that this is pretty much a duplicate posting. Ying Wang gave a decent layout on the other posting.

I'd combine the two bathroom spaces to make what you want, then turn the "back left" bedroom into a hall bath and walk-in closet. I'd probably keep the doors about where they are, but then the combined closet and left half of the upper bedroom become some mix of the new closet and maybe some extra MBR floor space.

The issue with the other posting is that there was no accessible water source other than getting it from downstairs which is cost prohibitive. Taking these two rooms also gives us more space.

This is a large, expensive project. I would find an architect or interior designer to come up with the best solution.

Since you are saying there's no water source in what was shown on your other posting, then you will probably need to make the back left bedroom your master.

Your current master would then house the expanded master bathroom and closet.