You can just take the hoses loose at the jack. There'll be some fluid dripping so have some rags handy. AND someway to keep dust/dirt out of the fittings.
Don't worry about high pressure or air in the hoses. When your finished cycling the system a few times will bleed the air out.
Here are a couple of YouTube's that might help.
Contact a hydraulic shop to see if they can rebuild your jack
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