I have found this in multIbit HD section..

Replace-by-fee (RBF) transactions
A change to Bitcoin Core in version 0.12+ involves replace-by-fee transaction support. RBF is an optional extension to a standard Bitcoin transaction that permits the sender to perform a repeat broadcast of an earlier failed transaction with a higher fee attached. Typically this is to "free up" an earlier transaction that has been accepted into the network as valid but because the fee is too low is being ignored by miners. Repeating the transaction with a higher fee allows the sender to override the earlier transaction in the hope that the miners will add it to a block.
MultiBit does not currently support the creation of these types of transactions and relies instead on setting an appropriate fee to the transaction to ensure timely inclusion.