I "accidentally" got hold of a few german websites. now I want to change the design. they are .php , where I have no clue of.

if I make the new site in html, are the old pages losing their ranking which is very decent and many pages have PR 2 and 3? What could be done to avoid that.

Hope it sounds understandable. Apologies if I use wrong terms, I am a beginner and try to get my head around that all since a few month