Step one: see what you have
Most people underestimate both how much they own and how much room it takes. The Item Scanner turns photos into a reviewed list with quantities and approximate sizes, which is the only reliable starting point.
Step two: decide what stays close
Once the list exists, splitting it is straightforward: things you use, things you use seasonally, and things you simply need to keep. Only the last two groups usually need to leave the house.
Step three: place it somewhere sensible
SpacePlanner arranges what is left into a specific space, so you can see whether the loft is enough or whether you need somewhere else. If you need somewhere else, Location Search shows what is actually published near you.