How to upgrade the HDD with a 7 mm SSD drive?

I have an Inspiron 1545 with its original HDD drive and I want to replace it by a new SSD unit. The main problem is that the original HDD has a height of 9.5 mm and the newest SSD units (like the Samsung 840 Evo) has a height of 7 mm. I know for several post in the web that the solution is to buy and attach an "SSD Spacer" to the disk. This piece of plastic ensures that the SSD will be recognized by the Laptop BIOS, but the problem is there is not a step by step guide that shows how to do it in the right way.