Tool to copy changes to production SQL db?

I'm mainly a programmer with basic SQL experience. Have an online website which uses MS SQL server express db. Every once in a while, I have to alter a table (add fields) but run into the issue where SQL server won't alter unless the table is re-created, which will obviously result in loss of data. Is there a free tool, that can automatically create new tables or alter tables while preserving the data? #sql #sqlserver