By default, you should have 2 GB of RAM minimum. Anything lower than that is subject to failure because the simple updater will take all the RAM. Yes, it might be possible to update the OS, but use the Apple Logo > Force quit to end all the running application. Expect to have terrible performance and if something goes bad, the MAC OS X will give you notifications about that, but I strongly suggest to add more RAM, preferably 8 GB or more.
