Possible to mix memory sizes on Inspiron 15R N5110?

I have an Inspiron 15R N5110 that came with only 3GB memory, configured with a 2GB stick in one slot and a 1GB stick in the other.  I would like to upgrade but want to spread the cost out a little.  Would it be possible to just replace the 1GB stick with a 4GB stick, leave the 2GB where it is and end up with a total of 6GB?  That should be enough for what I need to do with the machine and I figure I can always replace that 2GB stick later.  Would a 2GB and 4GB configuration work on this machine?