A profit warning from Tesco sent many UK supermarket stocks lower on Monday, but investors in the firm itself seemed to celebrate the appointment of a new boss, sending shares in the grocery giant higher.Tesco, the largest retailer in Britain and second-largest in the world with a market capitalisation of £23.6bn, was trading over 2% higher in afternoon trade.The stock's gains helped the UK food and drug retail sector in London to the top of the pile, offsetting falls in the shares of rival chains J Sainsbury and Wm Morrison, as well as online grocer Ocado.Tesco announced this morning that Chief Executive Officer (CEO) Philip Clarke, who has run the company since 2011, would be leaving later this year and will be replaced by Dave Lewis, a director at BSkyB who is also the President of Unilever's Personal Care division.The move comes as the grocery giant said current trading conditions "are more challenging than we anticipated" at the time of its first-quarter update in early June. It said the overall market is weaker and recent investments to cut prices and improve customer loyalty mean that sales and trading profit in the first half are "somewhat below expectations".Jonathan Jackson, Head of Equities at Killik & Co, believes that today's news is positive for Tesco, saying: "The current CEO has lost the confidence of many in the market, and a change is likely to be seen as the best move for the company."However, the gloomy assessment of current trading is likely to have dampened sentiment amongst investors or other retailers, who have also been struggling with the rising popularity of discounter chains such as Aldi and Lidl, along with the ongoing resilience of higher-priced Waitrose.Top performing sectors so far todayFood & Drug Retailers 3,707.18 +0.90%Technology Hardware & Equipment 1,021.14 +0.38%Mining 17,677.69 +0.35%Gas, Water & Multiutilities 6,032.41 +0.32%General Industrials 4,056.66 +0.13%Bottom performing sectors so far todayIndustrial Metals & Mining 1,215.64 -1.46%Oil Equipment, Services & Distribution 23,632.17 -1.38%Tobacco 39,815.17 -1.15%Real Estate Investment & Services 2,565.35 -0.93%Electronic & Electrical Equipment 3,729.09 -0.87%BC