Demi Lovato says working out has boosted her confidence.

The 'Heart Attack' hitmaker told PEOPLE.com: "I'm kind of getting some confidence with all the hard work I've put in, so I might go a little sexier this year. But not like, 'Mean Girls' slutty!"

The star, who is in a long-term relationship with former 'That 70s Show' star Wilmer Valderrama, usually prefers to wear scary costumes.

She said: "Last year, I wore a really long dress that was actually from my 'Let It Go' music video. I ripped it up, and I stained it with (fake) blood. I was a zombie! To me, that's more fun than having to worry about what you look like all night."

She added: "You only get to use fake blood once a year!"

Demi recently revealed how she met Wilmer, 34, for the first time four years ago.

She told And Pop: "I went to his house for a PSA [Public Service Announcement] shoot for Voto Latino in 2010. I was like, 'Oh my god. This guy is so attractive.' We started talking."

She added: "He is very good looking. He is my absolute best friend in the whole world, who I happen to be attracted to."