Delivery firm Ocado, whose biggest customer is Waitrose, is surging today after Goldman Sachs upgraded its rating to a 'buy', from 'hold', as the recent share price performance has provided investors with a good buying opportunity.However heading the other way is United Business Media, which has fallen 10% after adjusted pre-tax profit declined by 5.3% in 2010.Engineer and ceramics group Cookson is 7% higher after swinging to a £189m pre-tax profit in the 12 months ended 31 December, from a £21m loss in 2009.Housebuilder Persimmon is edging lower despite underlying profits being in line with January's prediction.Miners Kenmare Resources and Centamin Egypt are both making gains of over 6%.FTSE 250 - RisersCentamin Egypt Ltd. (CEY) 127.60p +7.68%Ocado Group (OCDO) 216.00p +7.46%Elementis (ELM) 134.10p +6.85%Cookson Group (CKSN) 698.50p +6.80%Kenmare Resources (KMR) 42.56p +6.13%Morgan Crucible Co (MGCR) 306.60p +5.80%Meggitt (MGGT) 352.10p +4.11%Spirent Communications (SPT) 162.00p +3.85%Imagination Technologies Group (IMG) 426.90p +3.84%Ashtead Group (AHT) 177.90p +3.79%FTSE 250 - FallersUnited Business Media Ltd. (UBM) 643.00p -9.75%Provident Financial (PFG) 980.50p -5.08%Hansen Transmissions International NV (DI) (HSN) 44.29p -4.83%Redrow (RDW) 130.30p -3.70%Gem Diamonds Ltd. (DI) (GEMD) 276.00p -3.46%Dairy Crest Group (DCG) 351.40p -2.95%Tate & Lyle (TATE) 563.50p -2.84%Forth Ports (FPT) 1,478.00p -2.83%Daejan Holdings (DJAN) 2,823.00p -2.66%Tullett Prebon (TLPR) 396.60p -2.58%