How to remove temp tables from SQL Server?
Temporary Tables are dropped when the session ends. So, they will be dropped when you close your SSMS window, or your application session ends.

If you are working in SSMS developing code (and keeping the session open) then you'll need to drop them explicitly via...

drop #tempTable


Another common method, to prevent you from attempting to drop a Temporary Table that doesn't exists, is to check if it exists first.

if object_id('tempdb..#tempTable') is not null
drop table #tempTable

create table #tempTable...
or
select into #tempTable


A note on some helper functions from Aaron Bertrand should be mentioned.