Hello Singh,
1.Where you want to delete all entries Unit or development or both clients?
2.If you want delete or reset all the documents entries means you need follow the entire reverse process ( cancel all the account documents / Billing/Reverse PGI /Delete deliveries/Delete sales orders...) its a lengthy process and also FI/MM consultants should involve in this.
3.you need to check with backdated postings with FI and MM consultants.
4. It depends upon the number entries and time period (from which date onward you created)to reset all the documents and then delete the configuration is a good idea but in fact its not require to delete all the entries because I hope you done everything in testing clients not in a live system.
Thanks,
Krishna.