I've just upgraded my ssd following:
http://henjinkutsu.com/text/pc/svd1121aj_ssd/
Also follow J Gray's advice above.
I fitted a Crucial M500 480GB:
http://www.amazon.co.uk/Crucial-CT480M500SSD3-Internal-including-Screws/dp/B00BQ8RHMO
I used an m-sata to sata enclosure in a usb sata disk enclosure and made a copy of my original disk using Clonezilla. YUMI will help you download and put this on a bootable USB flash disc.
Points to watch:
1. The only problematic part of the case disassembly is the loudspeaker grilles. You almost certainly will be unable to reattach them and the cloth underneath using the adhesive tape that fixes them, make sure you have something suitable to re-attach, your best bet might be to detach the grille whilst leaving the fabric in place, then cut a hole in the cloth to access the screw.
2. When you open the case, don't forget the cable that goes to the switches under the front panel, it's very fragile.
3. Disconnect the battery as one of the screws and mounting brackets is shared with the ssd.
4. The cable that obstructs the SSD is quite difficult to remove, I used a steel rod underneath and pressed from the top with my fingers to clamp and get a grip on the cable whilst gently pulling away from the connector, there are no latches, it's just a push fit.
5. The new SSD is a little difficult to insert in the connector because you need to plug it in without really being able to see whether the connectors are lined up.
It will probably will take you 1 to 2 hours, but it's relatively straight-forward despite the difficulties.