The "Delete Account" button at the bottom will delete iCloud content from your iPhone/iPad.
It will NOT delete the iCloud account and you can still access iCloud content from any web browser.
When you select "Delete Account" it will first notify you that doing so will delete Photo Stream content.
Next, it will notify you that "Docuements and Data" store on the cloud will be removed from your phone.
Next, it will ask you if you want to keep or delete the Contacts, Calendar and Reminder Data.
Don't worry, you are NOT deleting any content form the cloud. If you select "Delete" on each of the options above, it will be synced right back to your device if you set up iCloud again.