Mar 25, 2015 at 9:28 PM
Edited Mar 25, 2015 at 9:31 PM
Hard to say for sure without seeing code, but looks like a theme mod and there are a couple of places to check for starters.
The themes folder in the blog root should contain your theme folder, there are two files within your theme folder where any customisations are likely to have been made.
site.master and PostView.ascx.
When you first enter the blog via browser or when browsing by category or tag you see a couple of paragraphs of preamble following the blog title that aren't there when viewing a single post - this might make your task a little easier.
Perhaps start with the PostView file and look for two containers:
<div class ="headingbar">Your Offending H1</div>
<div class ="content blog">Preamble paragraphs and standard BlogEngine markup</div>
I don't know how comfortable you are with coding, but there may well be conditional code near to these divs that needs altering. Should you find code near these divs or code referencing them, it should be a simple fix, if you are familiar with coding.
Then you would ideally change the single post title to be within an H1 tag.
You might want to think about how to replace the blog title and preamble or just leave them in for anything that's not a single post view.