UPDATE using SQL Server

UPDATE using SQL Server

I have one table TABLE1 such as :
id_conv
=======
a
b
c
another table TABLE2 such as :
id | id_conv
============
1 | NULL
2 | NULL
3 | NULL
now I want to update the table TABLE2 with the values of TABLE1 like :
id | id_conv
============
1 | a
2 | b
3 | c
how can I do it?