once you have created your castle you can then upgrade it for greater benefits

click on the castle icon to open your castle and click on the upgrade castle button as shown below
Attachment 4949

another window will open showing eight different sections of the castle that are upgradable
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the first thing you need to upgrade is city hall once that is upgraded you will be able to start upgrading the other castle sections
the panel at the bottom shows your progress on the left and the level required in other sections of the castle to be able to upgrade
as u can see in the screen shot below. the castle section levels are green so the level requirement has been met
Attachment 4955

in order to upgrade you need castle build orders and castle wealth from contribution. the highlighted box on the left of the screen shot below tells you how many castle build orders you have while the one on the right shows how much wealth you have from contributions
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to get points to progress to upgrade you need to use castle build orders. enter the amount of of castle build orders you want to use in the box at the bottom on the left hand side of the panel and then click confirm as you can see in the second screen 1 castle order gives you 10 progress points you need 100 progress points to make city hall level two
Attachment 4959Attachment 4961

once you have 100 progress points and 10,000 contribution you can then upgrade city hall
it will then show what sections of the castle need to be upgraded to level 2 before you can upgrade city hall again
Attachment 4975

continue by upgrading the other sections of castle in the same way