ANSWER:

There are usually special trays on which you can screw an SSD and then screw the whole tray into a 3.5″ slot. Also common is the approach that the tray can fit either a 2.5″ SSD or a 3.5″ HDD. So no special precautions have to be taken.

These should come with your case. This part from the specs hints at the fact, that the trays come with the case and are used for both types of drive:

Specifications

• 8x 3,5 inch HDD trays, compatible with SSD

But you can also buy them separately:

• Newegg: StarTech BRACKET25 Adapter Kit to Mount 2.5″ HDD in 3.5″ Drive Bay

This german article is explaining how to build a full PC using your case. Luckily, they even provided a picture:

by Oliver Salzburg from http://superuser.com/questions/415623