select FORMAT(convert(datetime, '25/06/2018', 103), 'dd MMMM')

create function GetDateDaynMonth(@date varchar(20))
returns varchar(20)
as
begin
    declare @DaynMonth varchar (20)
SELECT @DaynMonth = FORMAT (convert(datetime, @date, 103), 'dd MMMM')
return @DaynMonth;
end
go

select dbo.GetDateDaynMonth('25/06/2018')