Move to a larger drive
I'm not sure about if you can just copy over. Why is your user folder on a separate drive?? Anyway. I do have another suggestion. I got an ssd drive to use for my main drive, cause it's like ten times faster. I then ordered this thing that is basically the same shape as a cd Rom drive, but it holds a laptop hard drive. I removed the cd Rom drive and replaced it with that, which holds a terabyte drive. I partitioned it in half. 500gb is for my time machine backup, and the other 500gb is for extra storage. Or "external", without being external. I don't use DVD or cd's anymore, so it made sense to me. Good luck.