To read settings for one instance:

<db2 install dir>/adm/db2set -i <instance>

and (as instance owner):

db2 get db cfg for <db2 instance>

or (as instance owner, retrieving more details):

db2 connect to <db2 database>
db2 get db cfg for <db2 instance> show detail

To read global settings:

<db2 install dir>/adm/db2set -g

db2 connect to <db2 database>
db2 "select tbspace, overhead, transferrate from syscat.tablespaces"
db2 get snapshot for tablespaces on <db2 database>

To drop an instance do (as root):

<db2 install dir>/instance/db2idrop <instance>