The 24 GB memory limit may have been a function of the maximum possible memory size per stick when you purchased your computer. In my case, I have a Dell XPS 9100 which was specified as having a 24 GB limit. It has six memory slots, and at the time came equipped with six 2 GB sticks for a total of 12 GB. I replaced all six sticks with compatible Crucial memory (8 GB per stick). Booted up and the full 48 GB were recognized and tested out just fine.
So the following questions may determine if your memory size can be increased:
1) what is the processor?
2) how many memory slots do you have?
3) is the memory divided into banks which must have matching (in size) memory sticks? In my case there were two banks of three slots each.
4) what is the largest memory you can purchase per stick that is compatible with your processor?
If you do a search, you may find blogs that indicate whether others have had success in pushing the memory size limit. It may be necessary to ensure that the BIOS has been updated to the latest version.
Ray