To elaborate on Austin’s answer: Not only are they soldered, but even if you have the experience to desolder the RAM and replace it with compatible, better RAM; the calcuator’s operating system couldn’t even utilize it. TI designed the OS to rely on having only 256kb of RAM. The same goes for the Archive storage as well. You wouldn’t get a CPU clock boost either.
If you want to increase the speed of your TI 84 Plus CE, there are a few programs that can help. One such program is the Advanced Wait State Change[|r] I wrote that reduces the wait states of the calculator and can make it up to 30% faster.