WhatsApp Help - How to delete more than one message at a time...

Hi there,
My ultimate aim is to print a hard copy of a WhatsApp conversation that has run over a period of 6 months. It's in aid of a Visa application for me and my girlfriend so it would be super-super-appreciated if anyone could help.

I'm running the app on my Android phone (HTC Desire).

I have been able to email the conversation to myself and retrieve the text file which is produced. However this seems to only cover about the last 4 months.

I have scrolled all the way back within the app to the date I would like to print from which makes me think the 'Email conversation' option can only send across a certain length of time as the data is still accessible even that far back because I am able to view it. If that makes sense.

I woke up this morning with the intention of deleting the latest messages all the way back about 3 months, hopefully bringing the oldest date in text file back too. After 2 minutes of deleting each message one by one I've realised just how epic this undertaking is going to be as each day over the past 3 months we have been chatting twice a day with a lot of back and forth.

Does anybody out there know how else I can go about it? Is it possible to delete messages by the day or by finding the WhatsApp data on the phone and bringing into a PC to delete or something along those lines? I'm really in need of advice and if anyone can help - even possible theories I could try - I would be really appreciative.

Thanks.