How to change the gallery URL of a Picasa web album?
https://picasaweb.google.com/12344567890 but I want it to be like this
There was an option for this before but I can't find it anymore.
If it ever was an option to change it's not available now. It appears that the big long number you're seeing is your Google+ ID. (It is for me, anyway.) I suppose that makes sense because they've been working on merging Picasaweb with Google+ Photos.
I don't know if people who've managed to get Google+ "vanity URLs" also have customized Picasaweb URLs.
If you want a customized URL for Picasaweb, I'm afraid your option at this point is to use one of the many URL redirection services.