Changing permalinks for all my posts

Hello,

I want to start using a different type of permalink for my new posts and also, change the permalinks of my old posts. For what I understood after doing some research first, I need to go to settings–Permalinks in WordPress and choose the one I want. Then, I will have to redirect all my old posts. And finally, re-index my website.

My questions are the following:

– Is this the right process to change the old permalinks and start using a new format?
– Once I change the permalink structure in settings all my old posts will have the new url?
– Are the re-directions going to affect the speed of my page and/or my SEO ranking?
– How do I re-index my website?

Thanks

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