To get a copy of your high school diploma, you will need to contact the school from which the diploma was first issued. You can also contact the Board of Education and ask for the student records office.
You may not be able to get a copy of your diploma, but you can get the transcripts from the school that you graduated from. and yes they may charge a fee. My schooled charged for sealed transcripts (ones that are sent on to schools), but I could get an unsealed copy for free.