List sequence assigned to primary key

I added a few records to a table and assigned numbers to the id field - now when I
try to add records properly, it says that it can't accept duplicate values on the
primary field (id)

Although there were only a few records and I could just redo them, I wonder if
there is another method (for future reference)

So here are my two questions

1. How can you list (find out) the sequence name assigned to a primary key?

2. How can you change that sequence value?

I searched a bunch of web sites but had trouble narrowing my search to less than
about 30,000 hits