If it was originally purchased directly from TurboTax, then you may be able to download the program again without another purchase, but I'm not 100% sure. If it is for a year prior to 2015, then it may not still be available.
It is a good idea to keep your records and documentation for at least 5-7 years in the event that the IRS questions something with your returns. However, it would be rare for them to go back that far because only the last 3 years of returns are still 'active' with the IRS and states.
