hi there!
Option 1. recover all the refrigerant if you are familiar with the process.

If there is a shut-oof valve on both inlet and outlet of receiver then apply this procedure
Option 2. Pumpdown the refigerant. meaning
1.-connect your gauges to the compressor valves while both on back seat.

2.-Front seat(close) the valve after the liquid receiver.
3.-adjust cut-out pressure on LP switch to cut at
pressure below vacuum.
4. connect your gauge manifold to the compressor valves (HP and LP). Use a vacuum pump to remove air from the gauge lines with the compressor valves front- seated(close).
5.Then open the valves to almost intermediate position which will allow reading to be registerred on the gauge scale and also allow you to quickly close them later.
6. Run the unit and pumpdown will begin if the compressor cut-out too early on the LP swith , then readjust the cut-out pressure to cut out at a pressure under vacuum. Close (Frontseat) inlet of receiver.You will not be able to recover the left over a 100%. Then the decision is left with you
7.When the compressor cuts-out on a pressure below vacuum, then quickly front-seat both compressor valves