Pretty easy really... just have to be very careful nothing goes down the little holes

since yours is already out just load it down with some wd40 and pull the injector out of the sleeve. The sleeves are delicate and brittle at this age so be gentle. There should be nothing glueing them in so if there is someone has hacked it.
My In car procedure:
I disconnect the fuel lines from the injectors. Then you can use a flat blade screw driver to pry the injector out of the red sleeves. The injectors have o-rings on them that you should replace.
The sleeves are peaned in place. That is they put them in then smacked the AL intake at the top 3 times around the hole to deform the intake pipe slightly and hold the sleeve in. You can use a puller to get them out if you want, but if they are intact w/ no cracks I'd leave them be. Keep in mind that each time you pull one out you risk some built up gunk/carbon falling into the valve seat if your intake is still on the car. Not a great risk, but be aware. If you replace one, use an automatic center punch and pean it into the intake pipe.
Enjoy!
-Michael
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Michael 
'82 Euro SC 'Track Rat' 22/29 Hollows, 22/22 Tarrets, Full ERPB F/R, Rennline Tri Brace, Glass bumpers, Pro 2000's, 5 pts, blah blah blah
'13 Cayenne GTS