“Renminbi” is the official name of the currency introduced by the Communist People’s Republic of China at the time of its foundation in 1949. It means “the people’s currency”.
“Yuan” is the name of a unit of the renminbi currency. Something may cost one yuan or 10 yuan. It would not be correct to say that it cost 10 renminbi.
A little confusing, but at least now you know.