Cant update from Enfold 3.2.2 to 4.5.1

Hello

I´m wondering if its possible to update Enfold theme from 3.2.2 to 4.5.1 without loosing custom CSS made on the old version that was not done as a child theme? And if so, how do I do that.

I´ve bought new version of Enfold and tried to update but haven´t been able to, the error message “update failed. A valid URL was not provided.

And also, the visual editor is not working in the current version.

Thank you