To edit an ad or to change it's location:
Go to My profile > Manage items.
Underneath your ad on the left side, there is an icon with 3 dots. Here, you can edit the ad, if the ad is active. At the bottom of the editing page, you can edit the current location of the ad to another location.
Please not: It's not allowed to create several ads with the same item in different locations. You must place the item in its real location to avoid misunderstandings with buyers about where the item can be picked up.