So today i was trying to delete a conversation that contained many old text messages, i've tried everything and nothing seems to work.
Yes, the time it takes to delete many threads cn be over an hour. I delete the shortest threads first. Than, I limit the messages to x# before they auto delete. I use SMS Backup to keep what I need. Delete the rest. The phone will freeze up while you are deleting messages.
Which phone do you have?
LG G2.
Open messaging app.
TAp menu button.
select delete threads
OR
select a particular thread, and tap menu button, then select delete messages.
Did you make sure the messages arent locked? if they are locked the phone wont delete them. Check to see if there is a little picture of a lock on the messages, if so thats your problem and you just need to click on them and unlock them before they can be deleted.