GUEST,Jennyr - don't be scared - go for it! To be honest, I don't think it really matters whether the strings are changed one at a time or all at once. In my experience, on my guitars, I've found that the guitar stays back in tune quicker if they're changed one at a time, rather than all in one go. But every guitar is different and, if you're not a gigging musician - where you might be playing later that day, for example - it hardly matters.