I would like to increase (or decrease) the amount of memory available to R. What are the methods for achieving this?
Microsoft Windows accepts any memory request from processes if it could be done.
There is no limit for the memory that can be provided to a process, except the Virtual Memory Size.
Virtual Memory Size is 4GB in 32bit systems for any processes, no matter how many applications you are running. Any processes can allocate up to 4GB memory in 32bit systems.
In practice, Windows automatically allocates some parts of allocated memory from RAM or page-file depending on processes requests and paging file mechanism.
But another limit is the size of paging file. If you have a small paging-file, you cannot allocated large memories. You could increase the size of paging file according to Microsoft to have more memory space.