Actualización de Memoria Ram en Dell XPS 9520

Crucial indicates you may use 5600, 5200 or 4800 MHz RAM, but it will downclock (run more slowly) to the maximum supported by your system. That system maximum may be 5200, or it may be 4800 as stated in Dell's specifications. Crucial indicates only that those three types of RAM will work in your laptop, but they don't say that they will work at their maximum designed speed.

You could look up your processor on Intel's site, to see what maximum frequency it supports. If it is 4800, then that's the maximum. But, even if the processor can support higher speed, that still may not be possible if the system doesn't support it. In other words, your RAM cannot run at a frequency faster than the processor supports. But, your system may have a maximum that is less than what the processor might otherwise be capable of.

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard. (Repeatedly touching a metal case part is not sufficient mitigation with modern components.)

If the system runs RAM at 4800 now, that's what any upgrade will run, even if it's capable of faster  operation;  the CPU controls the memory speed, and it cannot be upgraded.

Faster memory will simply downclock.

Do not purchase "gaming" or "high performance" RAM -- which is usually timed very aggressively.  That RAM won't work in your system.