Cant Delete Thread(s)

Hi Guys,

I've had my Samsung Galaxy S3 for approx 6 months now, and it has become laggy throughout the Text message app.

I've been looking around elsewhere, and I've (now) set my limit to 500 messages per thread, however I have threads which I haven't cleared since I started, and some people I send upto 20-30 messages a day, everyday, so you can imagine how many messages I have in some threads.

My problem is, every time I try and delete a thread, it doesnt do anything to delete a thread, but it will crash the messaging app - causing my to shut it down through the task manager, and reset the phone itself.

Are there any other tips to remove threads?

Cheers in advance!