Flow/Schematic diagram design from an existing .PPT

We have produced a flow/schematic diagram in .PPT but it requires a designers touch to make it visually appealing, easy to read and comprehend and to reflect our brand colours and style. The final image will be used on our website, as well as in PR materials. We may need a handful of iterations to get it right, but we work quickly and collaboratively, so this will not be an onerous or long-winded exercise.