Many people want to delete the FB chat, the reasons may be different, it all up to user. Messages deleting in Facebook is not easy as compare to deleting your sim text or emails. It is because FB keeps the history of your messages and facebook chat save.
If you want to delete your messages on Facebook then you have to open each message one by one, then from the option you have to select those messages that you want to delete. It will take a lot of time if you have many conversations.
There is another way as well, just delete all the messages from inbox. This is not a permanent method of removing messages because when the person sends you message again, it will reappear as the deleted will be archived.
Here is the complete guide the Facebook messages in slow and fast way.
Deleting facebook messages
Slow Mehtod
In this method, one by one you have to select each message and send them to the archive. In this way messages will disappear from your inbox but it will not delete permanently and reappear when someone send you the new mwssage.

You have to open every message separately one by one for deleting FB messages. Now, press the action option and then click on delete messages there.

After that, there will two options as Delete all and Delete selected. If you want to delete all messages then click on Deleted all otherwise delete selected.

Deleting Facebook messages
Fast Method
In this method you can delete all your FB messages in fast way. You need to use Facebook Fast Delete Messages extension page. You can use it on Google chrome by add to Google Chrome install button or you have to install it.

When you have successfully downloaded it then the extension will be active on your system. By using this extension, you can delete all your messages by clicking single icon.
When you open facebook by using extension then you see two new options on the top of the bar. When you use those options then your messages and converstion will delete permanently.

By using the extension, you can easily delete all the messages and the process is very simple, easy and time-saving.