This question has essentially been answered, it just means to make something more interesting. In some case, people who say someone is 'sexed up' mean they are dressed to more sexy. Like if a girl were to just wear the clothes she sleeps in to a party, maybe it is not so sexy. However if she puts on lots of makeup and wears great shoes and a sexy outfit, she is more 'sexed up.' It's not formal English though.

Sex up: To sex something up means to make it more interesting and exciting. (INFORMAL) They wanted to modernise the programme, sex it up.

Make more interesting.