Hi there,

You can change the text as you desired by creating language overrides.
Here is the language constant for the words you are looking for:
1. Don't have an account yet?
COM_EASYSOCIAL_LOGIN_NO_ACCOUNT

2. Register now and start interacting with people from this community today!
COM_EASYSOCIAL_LOGIN_REGISTER_NOW

You can refer to this documentation, there is some guidance on creating language overrides
https://stackideas.com/docs/easysocial/administrators/languages/creating-language-overrides