I am trying to change my Apple ID as the e-mail address that is used will soon be invalid. When following the instructions to sign out of iCloud, it tells me that all the information stored on this device will be lost. Is this the case?

Welcome to the Apple community.

The iCloud data on your device will be removed when you sign out, it won't be deleted from the cloud or any other device. When you sign back in again after updating your email address it will repopulate your device with your data from the cloud.

You don't need to change your Apple ID, you just need to change the e-mail address associated with the Apple ID. Having more than one Apple ID can be a pain as purchases made with your old Apple ID will be associated with that Apple ID and not your new one.

Apple ID - Manage