I need to change to California license, do I need an appointment?

You have to walk in. Go early like 6:00am in the morning and not early on Wednesday because DMV will stop taking walk ins at 3:30pm.

No you can go ahead and show up but you will be in line for a good part of the day. Even with appointment there is still a line but substantially less.

Best if you fill out the application online, then show up early, they will give you a window number, just show the confirmation number to the employee out front