July 8 (Reuters) - British soft drinks maker Britvic said on Monday it has agreed to be taken over by Carlsberg for 3.3 billion pounds ($4.23 billion), after the Danish brewer sweetened its bid. ($1 = 0.7808 pounds) (Reporting by Stine Jacobsen and Yadarisa Shabong; Editing by Sherry Jacob-Phillips and Rashmi Aich)