What type of computer is it?... The answer would depend on the type fo computer and forum where you wanted to post (or should have posted):
Storage forum:
If you're refering to Memory Space on Storage capacity, speaking of a Tablet PC(?), then 4GB may be all there is as this type of computers is not readily upgradeable....
Memory forum:
Speaking or a PC, Laptop/Notebook, or Netbooks, then you're speaking of 4GB of RAM Memory (4 Gigabytes or 4000 Megabytes of Random Access Memory, which is physical and temporary memory) and you can upgrade the amount of RAM Memory in larger modules or number of modules depending on the motherboard and OS being a 32 or 64 bit version.