Hi Friend,
If you do not have vCenter server then you can not use any option that "Tim" has specified.
I think, you are connected to your ESXi host through vSphere desktop client (aka VI client).
If you want to move your VM files folder, you have to follow below steps.
1. shutdown the VM
2. unregister the VM (right click the VM and click "Remove from inventory"
3. Go to datastore in which this VM files are there i.e. in your case starage A (which is local disk) , click on the VM files folder, and click on the option that I have specified on last screen shot.
4. Once you click on move option,. you will get list of other storage attached to that ESXi host. slect Storage B. click ok ..migration will start.
5. Once the move operation is over, register your VM again.
Let me know if you face any other issue.