Unless you've got a float valve to stop the pure water your system will be 'unpressurised' as soon as you switch it off, however you do that. After that the only pipes you need to take off are the membrane inlet (bottom) and the pure and waste outlets (top). After that you only need to take out the top 'plug' from the housing and you can pull the old membrane out - with a molegrip if necessary - you won't do any damage as the membrane is kaput anyway. The new membrane goes in exactly as the old one came out - be careful as they only fit one way round.