The question that comes to mind on this issue
How do i merge two blog?
What will happen to my old blog?

will there be dplicate content issuse?
What should i do before and after merged blogs together?

the old blog has some descent content.

You have to do many steps. Actually, I am telling you the way by which you can delete your one blog and the post of that blog will be moved to the second blog. This can be done by backing up and importing of the blog contents

Method of Merging two Blogs:

Let's take your first blog (which you want to merge with other) as 'a' and your second blog (in which you want 'a' merged) as 'b'.

Steps are following:

Go to 'a' Blog Blogger Dashboard > Settings > Other

Look for the 'Blog tools' import and backup under it, find 'backup blog' content.
Click on it and then, click on 'Download blog' button and now, Link: http://www.solenzoblog.com.ng/2016/11/how-to-merge-two-blogger-blogs-to-one.html