React Application Expo gramework with user validation Firebase Integration

I have an old versioned React application, built using React 15 with Expo framework and Firebase for memory storage. The application features user authentication and real-time updates.

I'm looking to update this application to the latest version of React with minimal code changes. The ideal freelancer will be well-versed in React, Expo framework, and Firebase. The project will involve the following tasks:

- Upgrading the React version: The application currently uses React 15. The successful freelancer will need to upgrade it to the latest version (React 17) while making minimal changes to the existing codebase.
- Ensuring compatibility: The updated application should maintain its user authentication and real-time update features.
- Performing integration: As the application utilizes Firebase as an integration cloud memory, the freelancer should ensure that the upgrade does not disrupt this functionality.

Ideal skills for this project include:
- Expertise in React and React Native
- Experience with Expo framework
- Proficiency in Firebase integration
- Ability to update an existing application while maintaining core features