I have a trial website on a basic plan. Is there an option to change the plan to basic plus within the trial or do I need to create a new site and copy the existing one?
Since this is a trial site we can actually help switch the site plan for you.
You can reach us via support chat or case and provide the site URL in question.
I just submitted a support request. hope it will be done soon.
As it's a trial site, there's no way to change the site plan from your partner portal or likewise. The only current option is to contact support as Sidney mentioned.