Windows 7: Upgrading to an SSD, worried about Windows 7

I have been thinking about upgrading to an SSD (I currently have 1TB mechanical hard drive). When I built my computer back in 2011, i bought the retail full copy of Windows 7 Home Premium 64 bit and installed it onto the 1TB hard drive. I am now considering buying an SSD but installing Windows 7 onto the SSD. I do still have the disc for Windows 7 Home Premium. I was wondering if I would have to buy Windows 7 again or could I just re-use the disc?

You can reuse, also clean install or transfer.

SSD - Install and Transfer the Operating System

YOu can reinstall retail Windows 7 wherever and as often as you want.

What I'd do is follow these same best practices for Clean Reinstall - Factory OEM Windows 7
to the SSD.

Depending upon the size of the SSD you'll want at least the programs on it, but if space is or becomes limited you can move to or leave your User folders on the HDD and simply link them from Windows 7 to their related Library - Include a Folder - Windows 7 Forums.

When ready to delete the OS on HDD, you can do this while keeping the data on it by shrinking the OS partition, moving the data to a new data partition you create then, then when ready delete in Disk Mgmt the old Windows 7 partition on HD to create a new partition, or resize the data partition into the deleted space: Partition Wizard Resize Partition Video Help.