For any method you will need a sharp big knife.
Method 1 to de-seed a pomegranate:
Roll the pomegranate to release the seeds. cut the pomegranate in half or in quarters. Hold it over a bowl and tap the skin with a wooden spoon. scoop out the seeds.
Cut off the top of the pomegranate and cut it into quarters along the wedge lines so the pomegranate seeds remain intact. Place pomegranate quarters in a bowl of chilled cold water, submerge it. Pull the skin off and pull apart seeds. The pith will float to top, discard it. The seeds will sink, drain them in a sieve, rinse and drain again.