So if your server instance has the default trance enabled, then you can find out who has changed what in you databases.
1. This Query gives the trace flie path.
SELECT * FROM ::fn_trace_getinfo(0)
2. Execute the Below Query to get the data from trace file. The filters can also be applied to the below query to get the exact data
SELECT * FROM ::fn_trace_gettable ('
3. Map the trace table to find what type of event has happened.
SELECT TE.name, T.*
FROM dbo.temp T -- table that contains the trace results
JOIN sys.trace_events TE ON T.EventClass = TE.trace_event_id
4. To get the list of possible events
SELECT * FROM sys.trace_events where name like '%alter%' ORDER BY trace_event_id