Man it'd be difficult, but part of me would be tempted. I'd be back in high-school, I'd work my ass off and graduate with better grades, I'd go and make sure my dog gets to the vet before her cancer gets bad (we discovered her cancer in 2011) and give her a good 5 more years of life without the suffering she had to go through with chemo and surgeries. I'd get a job and help out my dad with finances because I had no idea the debt was pilling on during those years, and I'd be tempted to avoid the whole relationship with my ex who was my first love but turned abusive when we moved in together. 5 years we were together. I'd chose a different study-field at Uni because I kind of rushed my decision making after I graduated.
On the other hand I'd have to time it right so that I'd be at the restaurant where I met my current girlfriend on the same date that I met her, and I'd feel manipulative by trying to get her back with me while knowing everything about her and her knowing nothing about me. I guess our chemistry would never be exactly the same as it was when we first met.
On the other hand its like all the bad shit that's happened and other shit that's happened has defined my life, and I guess it'd kind of suck to let go of all those memories as if they were just dreams from another life, and knowing that they were only ever real for me.