Which option do I choose to move the data I'd entered here:
Christmas Bush (Ceratopetalum gummiferum)

to this one:
Christmas Bush (Ceratopetalum gummiferum 'Albury's Red')

You can't really move data from one entry to another. Submit a data proposal for 'Albury's Red' and then submit a second data proposal for the species entry, leaving most of the data unchanged but deleting the information that pertains only to the cultivar.

thanks again Zuzu for your helpful tips.