When you install an SSD into an existing system, there are bios settings (for example AHCI), that need to be changed to take advantage of the SSD capabilities. Note, there are a few good "how-to" web pages that detail the settings needed, both in a new setup and in an existing set up. Also NOTE: AHCI must be set for SSD to be fully utilized, and this is NOT done automatically in an existing set up.
Also, of course there are settings in Windows that also need to be changed, for example the page file, and how the OS "Indexes" its files. There is no real need to index or have a page/swap file, because access is already as fast or faster than the equivalent spinning drive.
For me personally, I'd install a new SSD and reinstall the OS. Newer motherboards will adjust accordingly, as well when the OS is installed, will make the appropriate AHCI settings, trim and so forth.