Hello Wendy, "Hang out" is used in a more positive way meaning that you enjoy spending time with someone. "Hang around" is a bit negative since it implies that you are with someone or somewhere but you STILL wish to be somewhere else or with someone else.

Hi! "Hang out" implies that there was specific intent to spend time with the friend. "Hang around" indicates that it was a default choice taken only in the absence of other options. :)