PostgreSQL Processes on a linux box

Hello,

altered a database using DBVisualizer. When I hit execute,
DBVisualizer stoped working and no I have two processes on my server:
postgres 30873  0.0  0.7  46552  7124 ?        Ss   12:33   0:01
postgres: postgres dbName 10.0.1.198(53658) ALTER TABLE waiting
postgres 31007  0.0  0.6  46708  6500 ?        Ss   13:07   0:00
postgres: postgres dbName 10.0.1.198(53799) SELECT waiting

What can I do? OK, I can stop and start the Database, but I think
there are other ways to handle this...
What Tool can I use to kill such processes?

Thanks and greetings,
Stefan Sturm