Here's what I have gathered,

Two ways:

1) Just take the weight off. Many divers are overweighted so make sure you don't NEED the weight. At the end of a dive with a nearly empty tank, a completely deflated BCD, exhaling fully and without kicking you should just BARELY be able to sink. This will determine the least amount of weight needed for the current gear configuration. Drop a pound at a time until you absolutely can't sink.

2) Add other heavy things and reduce "floaty" things. Changing from aluminum tanks to steel tanks is the easiest way to drop 6-8 pounds from your belt. A thinner wetsuit or a one-piece instead of a 2-piece wetsuit would help but only if you could do without the extra thermal protection.