Updating three columns in temp table using a select statement

Hi,

I am currently using a temp table to pull data to look through and work on. I would like to be able to update the temp table using a select statement or even better to be able to update the base table.

I have 3 of the columns in the temp table populated from the base table, col1, col2, col3.
 Col4, col5 and col 6 need to be updated with the results of the select. If possible updating the relevant rows in the base table would be preferable
Any guidance would be appreciated.
Thank you.