The actress told Movieline that she is "ready for the next chapter" in her career.
"I feel very fortunate to have the job that I have, and I enjoy going to work every day, but I think we've all been ready for the next chapter for some time," she said. "And for me, that doesn't mean the next acting chapter. I'm just itching to... go to school again and do other things with my time."
21-year-old Grimes added that she did "not particularly" enjoy portraying the teenage angst of her character Annie.
"I went through all that many years ago," she explained. "So it's just dredging up old 14-year-old drama that I don't really care about or find relevant to my life at all, but it's what teens want to see, right?"
She went on to say that the CW series is still "very fun" for its intended audience.
"I'm not sure that anyone is learning life lessons from 90210 but I don't think that's why anyone tunes in to watch the show either," she said. "It keeps it entertaining. It's like a soap at night with a bunch of hot teens. Who wouldn't want to tune in?"
Last year, Grimes admitted that she was toying with the idea of leaving acting to launch her own fashion line.
90210 continues on Mondays at 8/7c on The CW in the US and on Tuesdays at 9pm on E4 in the UK.