My insignia tv gave up and somebody told me to change the power supply, any ideas how do i change it?

Ordinarily you wouldn't change it. A qualified servicer would change it. It very might be defective and need replacing. You identify it by the model , google the model for a parts list, get the part and google for a replacement. When you get it, pull the back off, locate the board like the one you bought and disassemble it, replace it, and replace the back. Cross your fingers, fire it up and hope you fixed it. If you smell smoke and it stays black all your work was in vain.