Each weekday, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period, including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates.

While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and company earnings forecasts. Objective elements include volatility of past operating revenue, financial strength and company cash flows.

Invesco

(IVZ) - Get Report

manages investments for institutional, retail and private-wealth clients. It has been downgraded to hold from buy. The company's EPS increased 40% in the second quarter over the year-earlier period, continuing a two-year pattern of EPS growth. Its revenue increased by 22.86% over the same time frame.

As a counter to these strengths, the company's return on equity has been disappointing. In the last 12 months, Invesco's stock price has risen 22.62%, outperforming the

S&P 500

. It is now relatively expensive compared with the rest of its industry, reducing its upside potential. Invesco had been rated a buy since August 2007.

Network computing infrastructure product and service solutions provider

Sun Microsystems

( JAVA) has been upgraded to buy from hold. The company has shown a pattern of EPS growth over the past two years, a trend TheStreet.com Ratings believes will continue. Net income swung to a profit of $329 million in the fourth quarter of its fiscal 2007 from a loss of $301 million a year earlier.

In addition, Sun Microsystems' debt-to-equity ratio of 0.18 is lower than the industry average, and the company maintains a quick ratio of 1.47, which illustrates the ability to avoid short-term cash problems. The company had been rated a hold since April 2007.

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Tibco Software

(TIBX)

is a business integration and process management company. It has been downgraded to hold from buy.

The company's revenue rose 7.6% in the second quarter over the year-earlier period, trailing the industry average of 18.5%. EPS decreased by 63.64% over the same time period to 4 cents a share. The company's return on equity is also disappointing, and its operating cash flow is weak. On a positive note, its debt-to-equity ratio of 0.06 is below that of the industry average. Tibco had been rated a buy since March 2006.

Fidelity National Financial

(FNF) - Get Report

offers title insurance, specialty insurance and claims management services. It has been downgraded to sell from hold. The company's net income declined 36% to $84.84 million in the second quarter over the year-earlier period. Its return on equity fell to 10.33% from 20.97% over the same period, a sign of major weakness.

Fidelity National's gross profit margin of 11.40% is extremely low, and its net profit margin of 5.70% trails the industry average. In addition, the company's share price has decreased by 21.60% over the past 12 months, in part reflecting the company's declining EPS. The fact that the stock is now selling for less than others in its industry in relation to its current earnings is not reason enough to justify a buy rating at this time. Fidelity National had been rated a hold since November 2006.

Regency Centers

(REG) - Get Report

, through its subsidiaries, owns, operates and develops community and neighborhood shopping centers. It has been upgraded to buy from hold.

The company's net income increased 33.0% to $49.28 million in the second quarter over the same period last year, and while revenue increased 4.1% in the same time frame, this growth trailed the industry average of 21.7%. Regency Centers' debt-to-equity ratio of 0.98 is lower than the industry average, implying that there has been relatively successful management of debt. While the company may harbor some minor weaknesses, they are unlikely to have a significant impact on results. Regency Centers had been rated a hold since August 2007.

Additional ratings changes are listed below.