jackarjun563 :
i have 2gb ddr3 ram and 1 slot available. how to upgradewith the available slot
Quick answer: get another 2GB DDR3 memory of preferably same brand, model and type and insert it into slot 2. Provided everything goes well, you should end up with 4GB of memory.
More detailed answer: Even if you do it, 4GB of memory is not nearly enough for most of today's tasks, and 8GB is the minimum you should go for.
But that depends on which exact model motherboard do you have - the maximum amount of supported memory is determined by your motherboard. Maybe it supports 8GB, maybe 16, maybe 32... but it might be that it also supports only 4GB if it is old. So a bit more of a context here might help.