How do I add the High-res PNG to the JPG Post
I´m uploading for the first time and even after reading the wiki
I´m a little confused, as to how to do some things.

I´ll just shorten them:

- how can I add an high-res PNG-Version of a picture
to the same already posted lower-res JPG-Version?
(I´d like to avoid double postings that way)

- is there a way to merge my own uploads or is a
complete repost is needed? (would be a nice function btw :P)
(not refering to parent posts)

- I uploaded a fairly large JPG (10,8mb - 7300x23625)
and it got scaled down to some 119kb losing all its quality
Is there a JPG size limit I missed?

Thank u in advance for any help~~
1. Every single image is a standalone post. If you want to replace an existing image with a better quality one (png, larger size, whatever) just upload the new one and mark the old one as the child of the new one (optionally tag it as duplicate if it's a direct duplicate).

2. No. Yes you have to repost. You can also use parent function to link the two together. See: howto:parent/child.

3. In your case it's because it's a "dakimakura" image. automatically hides the original resolution image of "dakimakura" post, even if you're the uploader. The image still exists on the server, you just can't see it.
Thank you very much for your reply!
That answered all of my questions~