Multiple question about the product Acer Nitro 5 AN515-58-50FK

When you open the back of the laptop you will see the memory is protected by a metal plate. Undo the single screw, and pop it open. This will reveal the two DDR5 SODIMM slots. As for the storage, there are two M.2 PCIe x4 slots, both of which fit Gen 4 SSDs up to 2TB.
If you have 8 DDR5 RAM 4800 MHz installed buy an identical DDR5 module so RAM will run in Dual Channel mode at 16GB total RAM 4800 MHz. But can buy any 8GB or 16GB DDR5 module without XPM profiles, don't buy Kingston HyperX or Corsair modules. Total RAM advised by ACER is 32GB.

Yes, opening the laptop and upgrading RAM and storage will void the Acer warranty but this policy depends on the country, if you ask Acer Services they will respond that it will void the warranty.

The warranty policy is applied differently in each country, in the Philippines I changed the HDD and that did not void my 1-year warranty when I asked Acer to reset the system, but it may be used to decline a request for a major repair like a new motherboard.

On the DDR4 or DDR5 RAM issue, best to download and install CPU-Z, run it and find out the specs of your current memory module if that is a DDR4 module than use the table at the top (below) if it is a DDR5 than use the table I sent you before or at the bottom below:

Instead of CPU-Z you can also run this command in the Command Prompt: wmic memorychip list full