Is there a tutorial for upgrading the ram?
As above if you have to ask this is not for you, and no.
Upgrading has three broad paths, maybe four depending how you categorise things.
RAM has its performance measured in three broad ways.
1) Capacity. How many megabytes.
2) Clock speed. How fast it runs, here more useful in overclocking than anything else if it is going to be useful at all. Far more relevant on PC and possibly some old consoles where lower performance stuff was picked for some models (see original xbox and how they made it cheaper).
3) Timings. Basically pointless in the modern world but RAM writes, reads and such do not happen instantly in one clock cycle. You can get RAM rated for fewer cycles and thus theoretically improve times. All tests though say basically nothing of note in modern architectures and more improvements from 1) and 2).
Your upgrades target one of those things, or multiple I guess.
You are more focused on capacity which is fair enough. I will assume you are not going to try to claw some back from the underlying OS.
The two options are
1) Nintendo or Nvidia picked higher capacity chips as they were going cheap and locked them down to appear lower capacity. Rare for RAM to be this and more a thing for CPUs and flash memory. Likewise it is probably not going to be a simple software lock or held pin.
2) You replace the RAM chips with higher capacity ones.
2a) If you can't find pin and protocol compatible ones you get to build a board to either interface, recreate (FPGA memory is probably not there for this right now for these kind of specs, future is a different matter and you could use it for older stuff to boost that) or otherwise adapt (with the bonus here of it likely being high performance electronics that cares about matched impedance and interference compared to the normal save chips, amplifiers and screen mods we see such things done for). Similar things are done for consoles with expansion ports or cartridges that boost things as well, us seeing it for the GBA and DS, though code handling gets mightily annoying and you probably want to save that for distinct aspects of data (in the case of the GBA and DS stuff it was more an extra bank of memory to store data that might have originated on a CD on systems being emulated/stuffed in RAM on the PC version of the game).
3) It has been noted some dev kits in the past have more memory than baseline systems (far easier to dev with if you can optimise after you have the loop down, and also provides space for running the debuggers which can matter when you have say 256 megs of RAM in your system where contemporary PCs were frequently more than 4 gigs). I don't know what goes for the Switch stuff but that it was not mentioned where it was more normal on say the original xbox or 360 then eh.
For 2 it is not like the PC either where your BIOS just works for this and as mentioned things are baked in at hardware level. Now as far as software goes and assuming we are not using 32 bit addressing (2^32 being 4 gigs for a non bankswitched/paged system, the temptation being if you have 4 gigs less some for the system that 32 bits are in and saves the hassle of dealing with 64 bit maths/data handling) I am more optimistic than some of the above as modern compilers and OSes (which the Switch is running) means you might even gain some out of the box support from the memory allocation handlers. Though with things being largely optimised for the lower counts rather than some serious garbage collection/optimisation/free memory ideal algo then that is going to be limited compared to real hacks to get games to spread out over memory or shove data in memory that it normally fetches (at cost to load time or something else) from the cartridge/NAND/SD/network/USB.
Anyway back to the BIOS thing I don't know whether the handling happens at hardware level or you can do it with a firmware (and OS) hack/replacement for the Switch.