Diversifying stocks

[Brock]

Lets say someone has some stocks. Not much, maybe just around $25,000 in 3 stocks. One small, one a little bigger and one that has about $20,000. The larger stock is set up to purchase more shares with the dividends. Is it wise to take money out of the larger one, (lets say $5,000), and purchase other stock with it? If other stock should be purchased, what should someone look for? I'm really green to all this, so please speak english. Thanks.