If you plan to migrate your current OS to SSD you will need a tool which will help you move the system to the new the disk. In most cases SSD will be smaller then your current disk, so the tool should be able to shrink partitions during the operation.
There is a lot of tools available, but most of them are not free. I have used EaseUS Todo Backup Free which includes this functionality. In my case the disk had 5 partitions, but the OS partition was the third one, but even that was not problem for the EaseUS Todo Backup. It automatically shrunk the third partition, great job!
After you install the software, just click Clone button on the top and start migration in a few seconds.