SET NOCOUNT ON;

SELECT
    'EXEC sp_rename ''' + TableName + '.' + OldKeyName + ''', ''' + KeyName + ''';'
FROM (
    SELECT  TableName = CASE WHEN s.name = 'dbo' THEN '' ELSE s.name + '.' END + t.name,
            KeyName = 'PK_' + s.name + '_' + t.name,
            OldKeyName = ix.name
    FROM sys.indexes ix
    JOIN sys.tables t on t.object_id = ix.object_id
    JOIN sys.schemas s on s.schema_id = t.schema_id
    WHERE ix.is_primary_key = 1
) x
WHERE KeyName <> OldKeyName