Do you have a lot of background processes? One way to increase your array size is to increase your OS's swap space.
For windows, here's the guide.
But note that swap space is significantly slower than using physical RAM. If you find yourself running into Memory Error, you could try to rework your matlab codes to delete temporary arrays, or design your code to read data from hard drive only when needed, such as via datastore. Here are some useful web pages:
