If the PostgreSQL instance is accessible from your machine, you can easily do this:
psql -h your_server your_databasename -f /path/to/yourfile.sql
If it is not, you can open a SSH connection (through Putty) with port fowarding from 127.0.0.1:5432
(or whatever is your PG port) to other port (could be 5432 if you don't have a PG server running locally), and them just use psql
to import the dump:
psql -h localhost -p <other port> your_databasename -f /path/to/yourfile.sql
Another solution, is to send the file to the server and import from there. To send it, you can use WinSCP, that send files through a SSH connection.
One more thing, if your file is too big, you can check the "Enable compression" checkbox at "Connection > SSH" on Putty.