Only if the phone isn't fit for purpose or isn't as described.
If it keeps crashing, then yes, I would say that its faulty and therefore you should get a replacement.
If the battery runs down after 2 days and they had advertised it as lasting 5, then again, I would say yes. However if they had advertised it as 2 days, no.
If you are not satisfied for no other reason than you don;t like it or the phone doesn't do what you want, then no, you can't change it.
Even then, I would assume that the network would provide you with another phone the same, I doubt they would let you change model.