Changing your Journal Post Titles may be hazardous to your Blog!
One of the main problems I see when helping Squarespace users is the enormous amount of 404 errors found in Google Webmaster tools. Usually, they either have very few if any, or they have half as many error pages as they do blog posts. And here’s the reason why- the title you create for your journal entry is used as part of your url. Here’s an example:
TITLE: I had a horible day at work.
URL: www.mysite.com/blog/i-had-a-horible-day-at-work.html
However, a month later you realize, “Oh no, I spelled horrible wrong. I need to fix that,” and subsequently you go back and correct your spelling. Now here is the kicker. Changing your Squarespace post title also changes the url of your post!
Title: I had a horrible day at work
URL: www.mysite.com/blog/i-had-a-horrible-day-at-work.html
Now, this may not be a big deal if you don’t have any links coming to this post. But if you have linked internally from another page or someone has linked to you from their website, anyone following that link will get a 404 error page.
Website Mangament -> Structure -> URL Shortcuts
The best course of action is to optimize your journal titles right the first time, but sometimes it just can’t be avoided. Instead, you need to use a 301 redirect . You can find the option in Website Management -> Structure -> URL Shortcuts. Also see this official Squarespace help article 
Squarespace 301 Redirect for 404 Pages
Redirect Checker Tool
You can use this Redirect Checker to make sure your Squarespace 301 Redirects are working correctly.
