Is there a difference? Actually, it a very simple choice, you can do any of the following if you want a room upgrade. First, you can ask an interior designer to come in and create a new look. Most interior designers will work on your budget and buy the furniture and decor from a retail outlet.
Your second choice is to get a furniture designer who will customize your furniture to fit your lifestyle. He will create a new look from scratch, and come up with new modern furniture design. He does not buy furniture, he makes them.
Your third choice is to either get both an interior designer and a furniture designer to work together in partnership, or get a furniture designer who can also design the interior of the room, and not just the furniture. In other words, someone who can carry two roles and not break down while doing so.