In Oracle VirtualBox, you can install and run as many virtual machine as you like – the only practical limits are disk space and memory.
Here are the steps to adjust the amount of memory that is allocated to a virtual machine in Oracle VirtualBox:
Ensure that the virtual machine is powered off.
Select the VM from the list and select Settings > System > Motherboard:
You should the Base Memory slider. Select the appropriate amount of memory for the virtual machine and click OK.
Power on the virtual machine in order for the changes to take effect.