There's a Wordpress plugin called "Simple 301 Redirects".

Go through Google's cached version of your site, using the site:yourdomain.com query.

Make a list of every single page Google has indexed that you moved, or deleted.

If you deleted it (404 errors), create a 301 in the plugin that redirects the 404 URL to the homepage.

If you moved the page Google has in their cache, create a 301 redirect to the new page, using the plugin.

Then, resubmit your sitemap to Google, and you should start seeing changes in a week, or so.

HTTP ERROR 403 (FORBIDDEN)
This error is similar to the 401 error, but note the difference between unauthorized and forbidden. In this case no login opportunity was available. This can for example happen if you try to access a (forbidden) directory on a website.
HTTP ERROR 404 (NOT FOUND)
Most people are bound to recognize this one. A 404 error happens when you try to access a resource on a web server (usually a web page) that doesn’t exist. Some reasons for this happening can for example be a broken link, a mistyped URL, or that the webmaster has moved the requested page somewhere else (or deleted it). To counter the ill effect of broken links, some websites set up custom pages for them (and some of those are really cool).
For 403 i think you should delete it
For 404 Like hello world, dont worry abt it if you make new permalinks

Don't go deleting pages off your site. You're going to cause more harm.

Damn, I see what Yukon was saying after a certain time in the night, things go downhill fast.

To counter the ill effect of broken links, you're really going to recommend creating more broken links? smdh

Not like you'll be back to see this, anyways.

If you didn't have any existing ranked pages or any decent backlinks worthy of ranking a page there's really nothing to worry about or do. The only reason to do a 301 would be to salvage backlinks.

If you had/have ranked pages you've got a lot to worry about, overhauling a sites URL structure is a bad idea when ranked pages are involved. Broken links can easily drop a page in the SERPs.

You could always run Screaming Frog looking for 404s.