Jack up the car and set it down on the jackstands. Remove the wheel and disk and caliper. Then slide the floorjack under the end of the control arm so that the underneath side of the ball joint is centered in the jack cup and put a little tension on it. Note the position of the control arm and don't let it go more than an inch below where it is. The spring should stay in place and the only question is whether you have room to unbolt the strut to remove and reinstall it. If you can't, then put it all back together and do it later when you have a spring compressor.
Why are you changing struts on such a new car? I hope that they are not the hydropneumatic ones that cost a fortune!

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Tom Hughes
St. Louis
84 300SD
92 300D
86 300SDL