If you don’t want to migrate your store manually, just use one of automated shopping cart migration services available on the market. I recommend use Next-Cart, as most secure and trustful
It can move your store to Prestashop with no data loss or duplication, keeping your Oscommercestore available to customers during migration process. There is no easier way to switch from OsCommerce to Prestashop
Try out Free Demo to test the quality of transfer.