If I understand your question you want to upgrade your RAM is that correct? You'll need to take out at least one module to make room for the replacement module. Your system can support upto 16 GB of RAM.
Your system came with 4GB (two 2GB modules), so taking out one 2GB module you could put in a 4GB or 8GB module giving you 6GB or 10GB total memory (respectfully). If you take out both modules and replace both with 4GB you will have 8GB and in the case of 8GB modules you will have a total of 16GB.