Who you can hire for the work will depend on the local building dept and what they will require in the way of drawings as making the window openings larger will definitely require permits, framing inspection, etc..

I'd suggest a window company. They will then contract an architect or designer as needed if that level of planning is required, but in my area and many others, a simple drawing showing how the new opening will be constructed is all that is needed to obtain the proper permits and guide the installation.

In the event that you really don't know what you want and are looking for guidance on placement, size, etc I could see an architect being helpful in that case, but if you know what you want and just need to take the next steps to make it happen, a window contractor should be able to help.

I agree awindow company will have installers and contracros but you do need a permit so make sure that the contractor is aware of what is needed Are yu going taller and wider or what? Can you post pics of your home as it is and a drawing of what you are planning post here in commentsDO NOT start another post

This is not a "just" project. You have to remove siding, and drywall, and reframe the walls. Plus install the windows, and fix all of that that was removed or damaged.

We replaced one very large round-top window with 2 double hungs in our family room. Even though it was a "small" job, we had an architect come in and draw what it would look like from both the inside and outside to make sure it looked good and was being supported correctly. It definitely is a bigger project than you might think, since you need to do repairs inside and out.