Mock-ups
What are mock-ups, defintion and links: Mock-ups are 'very early prototypes' made of cardboard or otherwise low-fidelity materials. The user, aided by the designer, may test the mock-up (imagining that it works) and thus provide valuable feedback about functionality/usability/understanding of the basic design idea/etc.
http://www.interaction-design.org/encyclopedia/mock-ups.html
General examples: http://mockupstogo.net/
1. You need to have a screen shots of the existing site and point into the images where do the usability problems occur (see example below; figure 1). You refer to your usability report to base and justify the problems.
2. After the presenting the existing site usability problems, you display the improvements and describe how they solve the problems mentioned (see figure 2).
Usability problems found in the usability tests executed alst spring about the use of KPE and is information presentation. 