What I mean is

• suppose you're uploading a comic or a set, yet the pages are out of order because someone else is also uploading or has uploaded another page; or
• you're mass uploading, and the next page uploaded first before the first one;
• and you can't upload that page because it's rendered as that post already exists, and the OCD in you wanted to sort that out.

Is it okay or not okay to delete that post because it's out of order and reupload it again?

No, you can order pools and sets (albeit I'm not experienced with sets) without having them in any particular order on site. It can either be done manually by adding each page from its respective post, or reorganized afterwards in the pool/set.

If it's a comic, use new pool, if it's a set, use new set. You have to make them before you can add to them.

And man, my AutoCorrect is dead or something. Pain in the ass to type right now...

alexyorim said:
What I mean is

• suppose you're uploading a comic or a set, yet the pages are out of order because someone else is also uploading another page; or
• you're mass uploading, and the next page uploaded first before the first one;
• and you can't upload that page because it's rendered as that post already exists, and the OCD in you wanted to sort that out.

Is it okay or not okay to delete that post because it's out of order and reupload it again?

https://e621.net/help/show/pools
If your uploading a comic or image set put them in the pool it belongs to, or create one if it's not been made. Then you should be able to reorder them correctly within the pool. Won't change the site order but will fix it within the pool it's in.
Removing a post doesn't mean you can upload it again. Typically a post that's been removed is locked out and "can't" be uploaded again unless it's a bigger or smaller version of the original upload on e621. So not really a way to reupload... an admin probably would be better at explaining.