Try this:

declare @t table (Jan int, Feb int, Mar int, April int)

insert @t

(Jan, Feb, Mar, April)

values

(1, 2, 3, 4)

select * from @t

select [month], value

from

(select Jan, Feb, Mar, April from @t) t

unpivot

(value for [month] in (Jan, Feb, Mar, April)) u