UK hospital, I need help

So, I was recently in hospital UK NHS (the hospital which I was initially going to give birth in as it is a 5 minute drive away) I was in with a kidney and water infection as I have bad kidneys😣

I am regularly in hospital but it is my first time being in since being pregnant. I am 18, and the nurses gave me a hard time taking the mick out of me being pregnant at this age the hospital it's self is so unclean, there was a commode left lying around with poo on it, the beds are hardly ever cleaned, I was sick and a bit got on the floor and it was there 2 days later. So I have decided I want to give birth in a different hospital which is a 20 minute drive away, but has a better maternity unit.

Would I have to let my midwife know I want to go to the different hospital, is it possible to change? What shall I do about changing do I just turn up there when I'm in labour or shall I discuss it with my midwife/GP?