In the words of Clint Eastwood in The Unforgiven... "Deserve's got nuthin ta do wit' it'"
You can't express to a client that they should pay more because you feel you are worth it. That's just poor negotiating. Emotion has little or nothing to do with financial negotiations, or at least it shouldn't. Pleas for more money because you "think you are worth it" or "your providing great value" or anything along those general, nondescript lines are amateur and hackneyed at best. No client gives a darn about what you "think you deserve". Clients are only interested in what they must pay to get what they need done.
If you want to revisit pricing, revisit pricing.
After further exploration into the scope and requirements of the project, I'm afraid we may need to revisit pricing. I realize I gave you a general estimate in a previous conversation before complete scope was understood. Now that I have a better grasp on deliverables and requirements, can we please discuss my compensation. I would love to find a figure that is satisfying to us both. At this time, I believe $xxxxx (per hour or whatever) is a more accurate representation of fees which will be incurred. I am completely open to discussion on the matter. Please let me know your thoughts or concerns. Thanks!
From there, you need to have your ducks in a row... hard, realistic, definitive reasons why you need more money. Things like - additional 10 hours to build A, additional license for third-party package B, etc.
No one, and I mean no one, is going to revisit pricing because you feel like you deserve more or because you are giving away too much value for a previously quoted price.
Also be aware, revisiting a previously discussed price to any degree could very well result in the client walking away. Some clients will... you have to be willing to accept that before asking for more money.