Deleting invoices before the current financial year

I have started using clearbooks since last Nov, it was more like a trial for us from Nov to Dec and we started using this for invoicing and purchases since Jan. It's been great, until lately we wanted to use clearbook to do our books as well. Please don't ask me why we didn't think of that right from the beginning, all I can say is the person who does our books couldn't get it work and she prefers sticking to her own method. However, I think it is a bit silly to have the function here and not using it, so I started looking into it.

It occurs to me that the entries I have put in the system is not going to be accurate since I didn't input everything before the 1st Jan 2015.

My question is, is it possible for me to delete all the invoices and purchases before 1st Apr 2015? I read about resetting the account, but that will also delete everything we put after the 1st Apr 2015, am I right?

I tried voiding the invoices but it said "You are trying to process a transaction prior to the opening accounting date." even after I changed the accounting date to 1 Apr 2015.

I am hoping there is a way I can have my account up to date without inputting everything from Apr.

Thanks!!