For windows users recommended to download and use the FTrainer instead. For Mac and Linux there is no trainer, so the most recommended method is using high lives files to practice. To use this file, go to the main folder of the game and replace your file8.sav file by this one. If you want to keep the file8, you can rename it to fileX.sav being X the number from 1 to 7 of the slot you want to place your practice file.