Problem with changing the status of an order

Hi guys

Pretty new to 2.0.1.0 so please excuse me if this has already been answered.
I am trying to edit customer orders when they have arrived and paid to change their status from Pending to Complete.
The problem I am facing is this:

An order has a total value of 8euro in goods and 4 euro in delivery charge. When I hit edit, the delivery cost charge gets removed from the total and there is no way of adding it back despite being selected. If i hit save then the price will end up being lower than what it was and this will mess up figures.

Is there any way to change this or this is how 2.0.1.0 works?

See screenshots

You do not need to edit the order to change the status. You can also just view the order and in the status tab change the status by adding order history, this is actually the better way to do it.

so simple.
genious! thanks mate