You can't move previous purchases to a different ID. They are permanently tied to the ID used to make the purchases. However, you can continue to use the existing ID for iTunes (and other services) and create a new iCloud account with a new ID; the IDs do not need to be the same. One other thing to be aware of is that all new accounts are assigned @icloud.com email addresses as @me.com addresses are no longer available.
If you want to migrate to a new account and keep your data, start by saving any photo stream photos that you want to keep to your camera roll (unless already there) by opening your my photo stream album, tapping Select, tapping the photos, tap the share icon (box with upward facing arrow), then tapping Save to Camera Roll. If you are syncing notes with iCloud that you want to keep, you'll need to open each of your notes and email them to yourself so you can later copy and paste the text into new notes created in your new account. Then go to Settings>iCloud, tap Delete Account, provide the password to turn off Find My iDevice and choose Keep on My iDevice when prompted. Then sign back in with a different Apple ID to create your new account and choose Merge to upload your data. When you turn on Mail in Settings>iCloud you will be asked to choose your new @icloud.com email address. (Type carefully as once created it cannot be changed.)