Appliance have ran out of memory and cannot turn on. So when I can turn on my appliance only a black screen appears. I've only allocated 16GB for the appliance and I think this is occurring because I've forgotten to empty my trash for a while. But now I can't access anything within the appliance. What should I do?
I had encountered the same issue, but that was pretty easy to get rid of. The screen of your Guest OS simply wont appear unless you click on that black screen. That's all.
However, if you really want to deal with increasing the memory, you mean primary memory and not secondary. Nonetheless, Here is a way to increase both of them.
In VirtualBox, This is referred to as Base Memory. Right click on the desired vm, go to
Settings -> System -> Base Memory
And then adjust the memory as you need.(Just remember that your host OS also needs to breathe RAM)
Secondary Memory is where your programs are stored even if the machine is turned off. I prefer doing dynamic allocation when installing the machine. And in case one forgets to do that, this link has some answers.
Hope that helps.