How do you update values in a table with UpdateAsync?

This code won't work, when you spawn and don't have existing data it will set a table of values for you. If you have data then it will update the data inside the table and add 10 to it but it won't work. It keeps overwriting everything and clearing the whole data saved within the key and making it '60' instead of the stats table.

How do you update table values in a table with UpdateAsync without having to copy and paste the whole table every single time and put all the tedious values in there again?

local DS = game:GetService('DataStoreService'):GetDataStore('1')

wait(2)

local data
local key = '1'

local success, ret = pcall(function()
    data = DS:GetAsync(key) 
end)

if data then
    local stats = data.stats
    local coins = stats.coins
    local gems = stats.gems

    DS:UpdateAsync(key, function(prev)
        return stats.coins + 10
    end)

    wait(1)

    for k, v in pairs(stats) do
        print(k,v)
    end
elseif not data then
    DS:SetAsync(key, {
        stats = {
            coins = 50;
            gems = 10;
        }
    })  
else
    error(ret)
end