Replacing or repairing Windows

[mckenzie]

We had the wit down all replaced 13 years ago when we did a major extension and refurbishment.
With hindsight, I'm not sure that we chose the best people for the job. I think we might have gone for the cheapest .

We are now left with some windows that don't open properly, some that are open a little and now won't shut and some that shut but only by brute force and then still not properly.

What are our options I wonder?
They are fairly standard UPVC (I think that's what it's called) and it's a 5 bedroomed house so we have quite a few Windows and patio doors in total.
I'll be honest; I have no idea at the moment how much it would cost to replace them all and I'm considering getting quotes to replace and quotes to repair and wondered if the good people of mumsnet might be able to give me some advice.
TIA

[mckenzie]

"Wit down" being Windows of course