The easiest way is to create 4 empty archives so the last four will be recycled.
By default the SQL Server keeps 6 logs and this can be configured to be be between 6 and 99.
You need to exec the following stored procedure on SQL Server.
EXEC sp_cycle_errorlog ;
or restart server 4 times.
You can also check the number of files you keep by going to:
SQL Management Studio -> SQL SErvers Logs -> right Click -> configure and check
Limit the number of error logs before they are recycled.