<p>My ender3 came with a BuildTak-clone surface, and as I was a little too vigorous in getting the print off the bed (I had failed to level right and printed a bit too tight to the bed, resulting in SUPER strong adhesion), I needed to replace it.</p>

<p>Peeling off the black was easy. The plastic sheet that held the glue was easy too... but how to clean up the bed to get the residue glue off and prepare for the new 3M sticker?</p>

Cleaning up the aluminium build platform was rather easy in a three step process as I figured out:
Preparation
Get the old bed-surface off and any film layers that stick to the original glue. Don't bother to try to scrape off the glue, it is wasted time.
Solvent
To remove the sticker's residue, I first tried heat and 70% isopropyl alcohol (aka isopropanol, 2-propanol), which was not very effective.
What did prove effective was nail-polish remover on the base of
acetone
. It worked like a charm to turn the sticky film into easily removable, goopy clumps. With small doses and a lot of rubbing/massaging it into the residue and careful use of the scraper, all the glue was gone after about half to three-quarters of an hour of work.
In subsequent replacement, I used
paint thinner
, which is more effective in goopifying the glue and allowing to scrape it off much faster. 10 minutes max.
Cleanup
After applying the generous amounts of nail polish remover, I thought that it might be best to get any of the additives that were meant to protect the skin off the bed - as well as the slight blue coloring - before applying the new tape. So I gave the aluminium a good wipe down with isopropanol.
In subsequent replacements I used ethanol 98 % to clean the bed before applying, just to make sure no fingerprints or glue residue creates bumps.
Applying the new bed surface was easy afterwards, and after a quick bed leveling, the printer runs like a charm again.