Look up your laptop model number and find the manual that tells you where the screws and hard drive are.
this person did a tutorial for opening an Acer Aspire S3 - https://www.youtube.com/watch?v=IO9YXLW7FdA
keep in mind that DIY usually voids warranties
if you are replacing the hard drive, make sure you have a method to reinstall the operating system in case you mess up.
After you have your backup plan, find a "sata to USB" adapter or an external hard drive case to plug in the ssd while you load the OS.
now find a ssd migration tool for your ssd brand. Install the driver for the ssd as well.
Samsung's tools are here - http://www.samsung.com/semiconductor/minisite/ssd/download/consumer.html
After you've used the adapter to migrate the data to the ssd, you can swap the drives. You should be able to spot the hard drive as soon as you get the plastic bottom off.
Put it back together and turn it on. It should go straight to your regular login screen. If it has any problems, then do a clean install and copy your files afterwards.