not able to change css class they are locked? how to unlock?

I am trying to use best carousel slide, but it making the last slide as active, how to make the first slide as active?

Use the top popup menu that shows up at the top the Preview window. That's where you open and close items that have that ability in order to edit them. Keep in mind if you forget to deactivate something, it will be open on the website when uploaded, so be sure to follow through on them to make sure that what you want open is open and so on.