To update the Budget with Actuals:
Navigate to Budgets & Cashflow > Budget Tools > Export
Select Actuals as your Data Source
Set the Period Range Month/Year for the date range you wish to update
Check the exported file to be confident the date ranges are correct, if you have future month columns with nil values, delete those columns from the spreadsheet, or they will overtype your future budget with nil values
Then import into the relevant Budget version.