I'm planning to go to Hawaii next week, so I need to go to the bank to exchange some yen for dollars.
Literal
Next-week Hawaii [to-に] go [intention-つもり] [because-なので], bank [to-へ] yen [object-を] a-little dollars [into-に] exchange [to-に] go-not-must.
A multi-clause practical sentence. なので ('because,' attached to plain form via な) is the reason connective — distinct from から (more subjective) or ので (slightly formal). 替える ('exchange') takes を for the thing given and に for the thing received — 'exchange yen for dollars.' 替えに行く is the 'go to do X' purpose structure.