Change in marital status reporting

I had been a US permanent resident since 1983 but have lost that status (I think) as I moved to Germany in 2013 when I retired and have not been back in the US sine 2015. I have been receiving SS retirement payments ever since 2013.

When I moved to Germany I was married to a German citizen (we married in Florida in 2010). We divorced in 2016.

I married again on Dec 18, 2018 to a Serbian citizen and we now live together in Germany.

I believe I need to report changes to my marital status to SSA. How do I do it?

Thank you.