How to change blogger "read more" :

By using Jump breaks you can show only a snippet of your post on your blog index page and archives.
Blogger will insert a read more link after each post so your readers can keep reading by clicking on this link.

How To Use Blogger Jump Breaks.

Actually there is two ways to use Jump Breaks.

1. If you use bloggers new post editor

If you use bloggers new post editor, ( you can use it by enabling it via the Settings tab at your blogger dashboard )
You’ll find that there is new icon on the tab called “Insert jump break”

So while writing your post just click with your cursor where you want to add the Read More Link, And then, click on “Insert jump break” icon.

2. If you don’t use the new blogger post editor

You can insert the read more link buy clicking on Edit Html tab while writing your new post,

And insert

<!-- more -->

where you want the read more link to appear.
do it’ll look like the next image.

How To Customize Blogger Jump Breaks.

You can change the text “ Read More > ” by going to Dashboard >> Layout >> then Edit the Blog Posts widget.

And change it to what ever you want.