Some SSD drives come as kits which include a usb adapter and software. You connect the SSD via usb and the program copies the HDD data onto the SSD. Then you replace the HDD with the SSD. This SSD should be same size or larger than the HDD. You will be amazed at the difference in speed once you fit the SSD.

Another alternative is to remove the HDD, fit the SSD and just do a fresh install of windows using a usb flash drive to boot from. Windows will run even faster but you will have to install all the correct drivers from the laptop website. Then connect the old HDD via a usb adapter to the laptop (now running Windows from the SSD) and copy off any files you need onto the internal SSD. You can also use the old HDD plus usb adapter as a backup drive