replacing the conservatory gutter?

the house we moved into in Oct has a conservatory which, apart from the house wall it attaches to has another full height brick wall. Throughout the winter we noticed mould on the plaster where the wall meets the conservatory roof. We had a look at the guttering- though the bad weather made this tricky. It all looked reasonably ok ( well no holes etc.) The problem is still there though. I wondered how difficult it is to replace the box? gutter ourselves and if there is somewhere that tells you how to????