These navigation links are only available in the Layout Template.If you have a Classic template you have to upgrade by going to Template---->Customize Design--->Upgrade to get them.

log in to your dashboard--> layout- -> Edit HTML-->check Expand Widget Templates.Now scroll down to where you see this:-

<!-- navigation -->
<b:include name='nextprev'/>

If you want to show them only at the top you can Cut these lines to remove to the Windows Clipboard.
or
If you want them both at the top and the bottom then do Copy.

Scroll up to find this code :

<b:includable id='main' var='top'>
<!-- posts -->
<div class='blog-posts'>

Paste the navigation code below the last line of the above code. Save Template and refresh your site.

If you want to customize them further you can change this code below as of your template :

#blog-pager-newer-link {
float: left;
}

#blog-pager-older-link {
float: right;
}

#blog-pager {
text-align: center;
}

Save Template and refresh your site.