If you are running previous version of DotShoppingCart, you could do the following steps to migrate to the new version.
1) Make a backup of all your stuffs for the current verion including installed folders and database
2) Find SQL migration scripts in the Migration folder of the download zip package. And then run the migration script to upgrade your database. You will need to find your current version by going to the store admin and checking the bottom. And then run the migration scripts starting from low to high. E.g. your current version is V3.0, you will need to run the following scripts one after another
MigrateV3.0ToV3.1.sql
MigrateV3.1ToV4.0.sql
3) Unzip the install package and merge your current configuration settings for files web.config, DSC.config into the new version.
4) If you have customization made into the existing files, you might want to merge your customization to the new version as well.
5) Copy the new version on top of the existing one.