Text Size problem

I'm not sure if this is right place or not, so sorry if it isn't.

I have a member who is posting guides, However, when they try to increase the size of the text, and post the message, the text size doesn't change it is just shown with the text size tags around it.

How do I fix?

You posted it already here:
https://help.forumotion.com/other-problems-f46/text-size-problem-t32528.htm

And there we answered it. You shouldn't post the same problem to many forums. If they're in the wrong place, a mod will move it. But that way you won't find the answers and it's hard to us to help you.