Mark's method is how I've seen this done countless times-----on big tractor-trailer rigs down to the smallest cars and trucks too.

If they need replaced personally I'd do all four at one time especially if they're original and/or have no grease fitting Zerks. Moog would also be my choice, found mine on Amazon for about $125 shipped (2 uppers, 2 lowers) Understand some brands are available without threaded holes for the grease fittings just like most OEM ball joints---be certain to specify.

Have to agree with CarrFamily about the Bilsteins----added them all the way around and they're quite the improvement.