The short answer is no, you can't replace the RAM on your Mac. Any additional storage you want to add must be done with external drives. As for RAM, or unified memory, as it's also known in Apple Silicon Macs, you keep what you get when you place an order. You must remove the battery before installing the additional memory and reinstall it after installing the memory. The following procedure includes all the necessary instructions for both parts of the process.
Apple has soldered RAM to the motherboard of MacBook Air laptops to make them thinner, so it's not possible to upgrade the MacBook Air's RAM. I will also explain how to determine what RAM your Mac has installed, if it can be upgraded, how to buy new memory for your Mac and, finally, how to install your new RAM on your Mac. Since Apple has started making memory unupgradeable, your only practical option to get more RAM on your Mac is to choose it when you buy your Mac. While all Mac Pros can be upgraded, you have to search for the model and year of the Mac device to see if you can add RAM to your MacBook Pro. In addition to checking your Mac's storage (including other Mac storage) and removing excess files, a RAM upgrade will revitalize your Mac and possibly extend its life.
The Mac slows down when it consumes a lot of memory, that is, when running applications demand more RAM than the Mac can provide. If RAM is too expensive or your Mac doesn't allow an upgrade, try a comprehensive performance tool to speed up your Mac and give it the boost you need. If you're using your Mac for more demanding tasks, such as editing 4K videos or gaming, you might need to increase the RAM up to 32 GB for smoother performance and to prevent your Mac from overheating. All Mac Pro computers have user-expandable memory, which means that you can upgrade the RAM on any Mac Pro model. The process for upgrading your Mac's memory (RAM) depends on the version of your Mac. Use Apple Support to check the memory specifications and maximum RAM capacity of your MacBook or MacBook Pro, iMac, Mac mini or Mac Pro.
The obvious solution would be to increase your Mac's RAM, but before we show you how to do that, let's make sure that your lack of RAM is actually causing your Mac to slow down.