I got a D in GE course

[mikemac]

be sure you comply with the UC requirements to notify them

Transfers: If you add or drop a course, fail to earn a C or better in a course or enroll in a new college after you submit your application, log back in and update your information online.

If you receive an offer of admission, be sure to confirm with the campus admission office that they are aware of the deficient grade or schedule changes. Although you must notify the campus of these changes, we cannot guarantee that a campus can go back to review an application after correspondence has been received. Make sure to save a copy of your correspondence just in case.
http://admission.universityofcalifornia.edu/how-to-apply/after-you-apply/index.html

You can likely do this in your mid-year update. You don’t want to be in a position where they only find out about this grade during the summer; if they then revoke your admission you’ll have no 4-year college to attend.

BTW if it was me and I thought I could pass the class if I retook it, that’s what I’d do since if you repeat the class it replaces the earlier grade.