You can move items freely within the Toolbox (by left click dragging them), but when it comes to the preset and sticker panels, the items are forced to list themselves alphabetically. Presets can be moved from one group to another, by right clicking on them and selecting "Move Item", but the Stickers can't. The only way to move a specific preset or sticker so that it appears higher on the list, is renaming it so that the lettering will alphabetically sort it at the top. So if your preset was named "Sponge", you might name it "A Sponge". It'll require resetting ArtRage to see changes. In some cases, like Presets or Stencils, you can just right click on the preset and select the "Rename Item" option, but in the case of the Sticker Sheets, you'll need to rename them from the folder their located in within your computers directory.
Nothing is easy to the unwilling.