Yes - but there are some important details to keep in mind before you go ahead.
You can definitely upgrade your broadband, but it means you'd start a brand new One Utility Bill contract.
E.g. If your current contract is 12 months, and you decide to upgrade broadband after 3 months, you'd start a new 12 month contract from the date you get your new broadband speed. h
Note: If you have Virgin Media, you can only upgrade speeds, not downgrade them.