I really would like you're guys advice?

Okay so I just finished my freshman year in high school, and I realized that I really need to change. I am sick of being trashy, and slutty. I used to be a really good girl, very good christian, and then I made new friends that changed me. And now that its summer time I want to change over break. I cut myself from those friends, doing more with the church but as for my clothes I need your help. My summer plan is to loose weight, change my style and focus on school and not worry about friends. I want to know how to dress classy, I want a nice well put together look, and stylish for a cheap price. I really need your help. Btww I'm a 16 year olf girl. Pleaseee help <3