Options to extend memory limit

Dear All, at the moment I am using R for calculations of large
databases.  Unfortunately, R only manages to complete certain
operations at some times, and not at others. I usually get the error
message "cannot allocate vector of size XX"

I am using the 64-bit version with Windows 7. While my computer has 8
RAM, I do have a feeling that R cannot use all of it.

Searching online, I found that you can increase the memory with the
options --max-mem-size/ --max-ppsize or change the environment
variable R_MAX_MEM_SIZE to "allow deep recursion or large and
complicated calculations to be done"

Unfortunately, I am not very knowledgable yet on how to use R and I
did not quite manage to use the commands successfully. Could you
please tell me whether these do make sense for my case and if so how
(and at what stage of the process) I can use them?