i had download and install a ori whatapps when the apps store have promotion limitied time for free..... when i m using 3gs

after i change iphone 4 , my friend help me JB and download a JB version of whatapps from installous and now i wanna update it to ori version .... but i wanna keep the record , how ? i affraid that if i install the ori , the JB version chat history will be no more ...... any ppl help me ? in simple way ?