You have to check that an SSD can fit in your laptop before.
Then, if it does, you can buy one and replace your current HDD, then install windows 8 again on it.
Did you get a Windows 8 installation CD when you purchased your laptop ? (normally you do)
You can use this CD to install Win8 again.
If not, you may have to download the ISO corresponding to the same version of Win8 you are running, then call MS to activate it using your OEM key (sticker at the bottom of your computer).
Regards.