Longman Dictionary of Contemporary English - up-

~ prefix 1 making something higher  (to upgrade a job (=make it higher in importance)) 2 (especially in adverbs and adjectives) at or towards the top or beginning of something  (uphill | upriver (=nearer to where the river starts)) 3 (especially in verbs) taking something from its place or turning it upside down  (an uprooted tree | She upended the bucket.) 4 (especially in adjectives and adverbs) at or towards the higher or better part of something  (up-market (=suitable for the higher social groups))  (- compare down­)