I installed the H&R lowering kit which comes with shorter links for the rear on my 4.6 several years ago. To install the front springs the strut has to be disassembled. You will need to compress the both the existing spring and the shorter one to do that. You will need a spring compressor that is available to rent at most auto parts stores. The job is straight forward otherwise. At least the wheel you are working on will have to be off the ground. You will also need to have a full alignment done when you are finished. The following will give you an idea of the DIY. It is a 4.8 so ignore anything concerning air shock Also, no need to remove any fuses, you can easily get by without a bicycle wrench and he is overly cautious about damaging other parts. Not the best DIY video but all I could find. There are also DIYs that you can search out here.
BMW X5 Air Strut Replacement DIY Guide - YouTube