How do remove and replace the spark plug tube gaskets on the valve cover.

Pull harder. They'll come off. If not, buy a new valve cover.

They make spark plug wire pullers. Those can help sometimes, but typically, the suggestion of "pull harder" is what does the trick. Worse case scenario, take it to a shop and pay someone else to deal with the headache.

what bolts should be removed ?

The valve cover won't need the replacing, it'll be the spark plug tube! Believe me, because I took your lame advice, against my better judgment! Listen EVERYONE, do NOT force them to come out.If you look closely, just behind the spark plug tubes, after you gently pull the wire clips from the right side of the tube,(push down on the little clip and it will slide off) you will see a rail just above the tubes and to the rear of them. That contains the little wires to the plug you just removed. And it is DIRECTLY in the path of the lip that holds your gasket tight to the valve cover especially the two right plugs do the left ones first, they came right out for me.For the right two I noticed, (to late) that if you use one hand to push the rail back, you can pull the plug tubes up and out as easily as the first two! In retrospect, unless your daddy is buying all your parts and you don't care what it costs him, DO NOT take Alex's advice! And buying a valve cover to change spark plugs, just show's some people shouldn't be permitted to post anything on a serious site.