There is no change transaction type.

Transactions are defined as a list of inputs consumed, and outputs created, and the values assigned to those new outputs. The creator typically makes an output for a entity they wish to pay, and another output which pays excess change back to them.

Any amount of Bitcoin left un-used by the outputs is interpreted as the fee for the transaction.

Transactions have to spend all their inputs immediately. Essentially, any transaction splits the inputs to (at least) two destinations: the transaction's intended recipient and yourself (change).

Say you have an input with 1BTC and want to spend 0.5BTC:

                         ------- 0.5BTC (recipient)
1BTC  ---transaction----|
                         ------- 0.5BTC (change to yourself)

Any portions of the input that you don't designate to a destination become part of the transaction fee which will be claimed by the miner.