First step is to show coin control features... this will allow you to see your "inputs of coins."

If you have been staking for a while, its possible you have MANY inputs under the same address.

To divide or combine blocks, you need to select certain inputs, and send desired amounts of coins to your OWN address.

If you are sending less coins than your inputs selected, use a Custom Change Address and input your OWN address into that field. That way what is ever left over from the amount you choose to send to yourself as a "Block or Input," if there is any change it goes back to your same address. Otherwise it will create a completely new address for the "change" left over from the transaction.