How to increase the version number from 2.1.0 to 2.1.1 in vb.net : recently I'm working on my work, which is a maintenance system for various application, and I'm stuck at the arithmetic problem.

For the application version which is 2.1.0 now, and i want to update the application version to 2.1.1, the datatype of the version is stored as string, How does the algorithm for this change?