I've posted some of my FG for a star upgrade, but want to remove it. Anyway how to do so? or it forever posted until it sells.

It is unfortunately final and cannot be cancelled
Same thing applies in the DF for star upgrades

As mentioned above these cannot be cancelled. It is also stated in the sticky in that section here https://forums.d2jsp.org/topic.php?t=86575560&f=43

You can always shoot me a PM if you have any further questions