After some bathroom layout ideas

That is the funkiest shower recess I have ever seen. Keep it and build the rest around it. Just need a touch of lime green or yellow somewhere.

The easiest way to do it is to minimise the movement of the major services that cost a lot to move and create the most disruption to the exisiting space if you do. Therefore, work with existing plumbing and electrical. That said, if you have wooden floors, and the space underneath is accessible, that may not matter so much. Outside of that, you would need to state what it is you are trying to achieve with the renovation - in other words, write yourself and your designer/trademen a simple design brief, listing what you don't like about the current or what you would like from the new.