Still can't seem to find the answer

I have a Classic castle & would like to make a custom one...Can the Classic version be changed...Also, on my house storage summary; it shows a 1 in the used by moving crate...Any help or advise would be appreciated... 

Use the menu and get the item out of the moving crate.  Yes if properly placed a classic castle can be converted.  That is the reason they made new look Castles and Keeps.

Have to remove all the house only items.

So you have to empty the castles before converting? 

Not empty. But you have to remove all deeded items, house only items, and any floor tiles or walls.  There is a list of stuff you cant leave in it or it will not convert.

I would put all your containers in a spot where there is open space in the new design.  So walls will not cause any issues.

Before you convert a Keep or Castle you need to make sure that:

Items to Re-deed for Customization

• Steward, Mannequin, Personal Attendant, Parrots
• Raised Garden Bed, Field Garden Bed, Garden House
• Aquariums of all types and sizes
• Davie's Locker, Jewelry Box
• Koi Pond, Water Wheel
• All Crafting Stations, Gadgetry Table, Woodworker's Bench
• Blessed Statue, Fountain of Life
• Lighthhouse, check for linked ships first
• Bulk Order Deed Books, Alacrity Books and Transcendence Books should be placed into chests

Items to Stow Away

• Carpet, snow, grass, sand, water, or lava tiles
• All Masonry crafted pavers, walls, steps, blocks, and secret doors
• All added doors of any type
• Teleport Tiles (both Veteran and Origin bought)

These are not comprehensive lists and may change. If in doubt about something, redeed and put it in your bank until you are satisfied with your selected design.

Secure Replacement

• Castles cannot be converted into a customization plot (AKA custom home), only Securely Replaced or destroyed
• Double click the house sign, navigate to the Customization portion
• If the house is properly placed and the option to Securely Replace is not greyed out, proceed

• Click the Securely Replace This House option

• A system check will be made to ensure the replacement can take place
• An error message will appear if any of the previously listed items are still placed in the structure
• Only one error type will display per check
  • In the example gump, if the Stewards are removed, then a new check is made and the structure is still in error state, the new gump will display what is causing the issue. This will continue until a successful check is made.

• When successful, a warning will appear to ensure the decision to the structure

• For castles, only available castle designs will show. For keeps, only available keep designs will show.
• This function does not convert the structure into anything other than what it is. Ergo, one cannot go from a castle to a keep or a keep to a castle.
• Once selected, the new design will be put into place. All items will be located in the Moving Crate and the house owner will be alerted to the presence of Vendors (if any) that need placement.

Other Notes

• All Vendors will be put into storage with their inventory. After the design is complete, a message alerting the owner that vendors are available will be given. This is the only way to move a vendor in a castle or keep, so be sure they are placed where you want them.
• All items that are locked down, deeded, or secured will go into the Moving Crate which can be found via the House Gump. The boxes within the crate will lay atop one another in the Classic Client and cannot be rearranged within the crate. Items can only be moved out of the crate.
• See House customization for related information.

AtlanticRealtor said:

Before you convert a Keep or Castle you need to make sure that:
...

Very nice guide!  I don't have a castle or keep, but it's still nice to have all that info in one place.

I dont think Jewelry box is a deed.  You have to remove jewelry box also. That could be a pain if full.  Took me a long time to find a fireflies that I had on a wall when I was converting.

Very helpful thank you all very much ! 

Thanks all...It worked...I never would have figured it out without your help...Thanks again...