use tempdb
create table #tg (i int primary key, vc varchar(10))
go
select CHARACTER_MAXIMUM_LENGTH 
from information_schema.columns 
where table_name like '#tg%' 
and column_name = 'vc'

print 'alter table #tg alter column vc varchar(15)' 
alter table #tg alter column vc varchar(15)

go
select CHARACTER_MAXIMUM_LENGTH 
from information_schema.columns 
where table_name like '#tg%' 
and column_name = 'vc'

go
drop table #tg

OUTPUT:
CHARACTER_MAXIMUM_LENGTH
------------------------
10

alter table #tg alter column vc varchar(15)

CHARACTER_MAXIMUM_LENGTH
------------------------
15