means Cheerful, optimistic, and full of positive energy.

from Straight from music: the 'upbeat' is the unaccented beat in a bar, marked by the conductor lifting the baton upward before the strong downbeat. By the early 20th century in American English, that rising gesture had drifted into figurative use — a lift of the spirits rather than the hand — and 'upbeat' came to mean buoyant and hopeful.