Segregated Witness (SegWit) improves transaction malleability and capacity in Litecoin by separating the witness data from the transaction data. This separation removes the witness data from the transaction block, reducing the size of each transaction, which in turn increases the capacity of the blockchain to process more transactions. Additionally, segregating the witness data helps prevent transaction malleability, which is a vulnerability that allows attackers to change the transaction ID without altering the transaction's content. By addressing these issues, SegWit enhances the efficiency and security of transactions on the Litecoin network.