Rita changes her way of speaking because she wants to talk properly. Frank doesn´t like it at all, he wants her to be herself.
Frank and Rita have different views on what means to talk properly.
Rita thinks that talking properly means talking in a sophisticated way, using fancy language and posh accent (in my mind I believe that it would sound like that).
Frank thinks that talking properly means talking the way she usually did, with slung language, talking fast and without caring what others think of her.
This, among other changes, is what Frank has been fearing all along: how much of the new environment has Rita acquired and up to what extent should she do it.
Should she change completely?
Franks fears for her, he never wanted her to change (although in the previous scene, he was excited by these new changes). In this scene, we can see the side effects of the changes, so to speak.
Frank has given Rita so much freedom in her choosing that now he doesn´t know how to cope with the new Rita. A very defiant Rita , trying to show Frank that she is now a little innocent girl any more, that she can take care of herself now.
Act 2 - Scene 2 & 3, Question 1
