[I cannot rez an object because my "parcel is too full." What can I do?]

I am trying to rez an object but keep getting an error message saying my parcel is too full. What do I need to do to fix this?

[I have a Linden Home, can I build walls inside to make a bathroom, kitchen or other separate room?]

If I have a 2 floor open space linden home can I build walls inside to divide some of it into rooms and if so how do you do that?