Link：Enable Version Control for SharePoint 2010 Document Libraries
Document libraries support version control at several levels. By default, versioning is not enabled, but is enabled in the document library settings.
Versions are complete copies of the document, not deltas.
To enable versioning, perform the following steps:
1. Navigate to the document library by clicking on its title.
2. In the document library, select Library Tools, Library on the management Ribbon for the document library.
3. Select Library Settings in the Settings section.
4. Under General Settings, select Versioning Settings.
5. Select the versioning options required, under Document Version History.
Note that you should ensure any versioning strategy you implement should meet any document management and retention policies enforced by your company.