You can't.
Security of a MultiBit wallet is broken into four parts:
- A wallet encrypted by the password but not the wallet words
- A wallet backup, kept in the cloud, encrypted by the password and the wallet words.
- "Wallet words," kept on a piece of paper
- A password, kept in your head.
You have 2 and 4, but not 1 or 3. My understanding is that that's not enough to restore your wallet. If you had your wallet words, or access to the computer that created this wallet, it would be different.