Help Needed For Changing My Blog’s Content

Hi guys,
I need help…
My Blog: http://ketchupandcaviar.com/
I like to change its theme. My blog already alive for the past 5 years with the same content and those are well indexed in google, if I change all those content whether it will affect my blog's PR? and also please suggest how can I build back-link easily for my blog?
Thanks and looking for your suggestion guys!
Help Needed For Changing My Blog's Content

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