How to increace nightly backup speed

I need to create nightly backups to separate computer over internet from 8.1
server

I tried to run pg_dump to make backup using command

"..\pg_dump\pg_dump.exe" -i -Z9 -b -v -f "C:\061127 mybackup.backup" -F c -h
81.50.12.18 -U myuser -p 5431 mydb

but this takes 4.5 hours to complete.

How to increace backup speed ?

Andrus.