Help I am preparing to replace my double glazed units after finding out that i can get the units for about 8% of the cost of replacing the entire window , However i am not the experienced DIYer and could use a step by step guide of how to knock out and fit back in, where to measure and what tolerance to allow so i don't have to rely on someone else coming out. A list of what i will need and how much i can expect to pay for them.