Using a socket wrench to hold the nuts, unscrew the two tank bolts with a screwdriver.

When reattaching the tank, tighten the bolts with a screwdriver, rather than tightening the nuts. Alternately tighten each bolt in increments, until the tank fits snugly against the toilet.

Avoid over-tightening the tank bolts. Too much force can easily crack the toilet tank or toilet bowl.