The stuff you will need to upgrade the hard drive in your laptop to a speedy SSD while keeping your Windows 7 installation intact are (besides the obvious SSD and laptop) a small screwdriver and an app for cloning your hard drive's contents onto the new drive. If you are looking at a large SSD, this part may ironically be more expensive than the laptop itself.
To get your existing data over to the new drive you also need an external USB hard drive case. Some would say that you also need an anti-static wrist strap, but during the 15 years or so that I've tinkered with computers I have never used one. I'll throw in a disclaimer anyway just in case:
Perform the following steps at your own risk. In some rare cases, swapping out the drive on your own voids the warranty, so check up on that also.
Cloning Your Hard Drive
That said, let's move on to the practical details. If you want to transfer an identical copy of your existing drive with the operating system and all your files to the new drive (without reinstalling Windows), the first thing you need to do is clone the hard drive (if you'd rather perform a clean install you can skip to the next step right away).
This could be a problem. If your hard drive has a larger capacity than the SSD and the data on it exceeds what the SSD can store you will have to backup parts of the drive's contents before you clone the drive.
When this potential problem has been solved you need to insert your new SSD into an external USB hard drive enclosure. These are available in just about every store that sells computer peripherals for about $20. Inserting the drive in the enclosure is very easy using the aforementioned screwdriver. A simple manual on how to do this should also be provided with the enclosure.
Once the drive is hooked up to your computer you will need special software to make an exact copy of your hard drive to the SSD.
NOTE: This guide previously used (and suggested) a free trial version of Acronis True Image, which worked at the time of writing. However, as indicated by readers (thank you) this feature is no longer available in the trial version so I removed the link.
As an alternative, EaseUS Todo Backup still offers drive cloning as part of the free version. It can be downloaded here.
Once installed, click the "Clone" link in the application, which brings up a handy wizard for drive cloning. After selecting the source drive, remember to tick the box "Optimize for SSD".