How do you increase the amount of RAM that Lightroom can use? My laptop has 16gb of RAM and Lightroom is incredibly slow. I'd like to increase the amount of RAM that Lightroom has available from the default 2gb to around 10gb, but can not find the area to make that adjustment.
I don't believe you can.
There are no user-level settings to control the amount of RAM used by Lightroom.
If you are using an older 32-bit version then you are limited to 3-4 gig as a requirement of that architecture.
LR will use as much RAM as it needs. The reason LR CC/6 is slow is not because it doesn't or won't use all available RAM you have installed.
It is because you have the Use Graphics Processor turned on. Turn that option off and test. That option is found in the LR Preferences under the performance tab.