Yes there are two ways in Dorico 4:
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Get to the second picture, select the half rest in the pick-up, press Shift-B for the bars and barlines popover, enter -2q (to remove two quarter note beats), press Return.
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Going from the very beginning (so starting from your first picture), select the half rest at the start of the bar, active Insert mode, set the scope to Global Adjustment of Current Bar, then press Delete (or Backspace, but either way just one of the standard delete keys). Dorico removes the selected amount of time from the flow (ie a half beat) and updates the time signature; because this is the first bar, it gets converted into a pick-up.