。
I'll change my shirt.
Literal
I [topic-は] shirt [object-を] change.
取り替える ('to exchange, to replace, to swap') is a compound verb — 取る ('take') + 替える ('swap/replace'). The 取り here acts as a prefix strengthening the verb meaning 'take (and replace).' Japanese compound verbs like this are highly productive and a major source of vocabulary.