Switch different versions of cuda in win10

I install cuda7.5 and cuda8.0 in Win10,how do I switch between different versions?

Normally by changing the CUDA_PATH environment variable before building your projects and solutions.

I switch the version of cuda to use tensorflow,so I do not need to build a project or solution.

This seems to be a question about configuring Tensorflow, rather than a question about CUDA. As such, you will likely get better answers by asking in a forum / mailing list dedicated to Tensorflow.