If you purchased the TurboTax software as a download then you need to sign onto your download account here - https://shopping.turbotax.intuit.com/unified/downloads?route=myaccounts&cgcview=downloads
How did you install it the first time? Did you use the CD or do the download method? If you used the CD you may have a problem. Otherwise you download it the same way.
Access your downloads here
https://shop.turbotax.intuit.com/commerce/account/secure/login.jsp?pagecontext=download
How to download your software purchase
Did you purchase the download from TurboTax.com or somewhere else? You have to redownload it from the same place where you originally purchased it.
When you sign in to your downloads, make sure you are using the exact same user ID that you used when you purchased the download. Many people have more than one TurboTax account, sometimes without realizing it, and the user IDs might be similar. Follow the instructions in the FAQ at the link below to get a list of all your TurboTax accounts. If you have more than one email address, do it for each address. Before you start this procedure, make sure you are signed out of all your accounts, including the one you are using here in the Community. You can access the FAQ without being signed in.
How many Intuit accounts do I have with TurboTax?