How does a pilot receive weather information when overflying the oceans?
It depends on what info you're after: During cruise I'm mainly interested in threats to the aircraft which normally manifest as echo on the weather radar (clear air turbulence being one famous exception) or by looking out of the window. 


Do you want info on your destination and alternate airport you listen to a HF VOLMET station or ask ATC via HF (cumbersome and annoying due to often poor reception). 
In our shiny new world we could also ask ATC via an CPDLC free text message. The controller simply uplinks you a message with the requested information.
Depending on your operator there might be a plethora of other information available via ACARS which - when equipped - can communicate via satellite. At my company we can get:


Updates on the winds aloft (important for fuel calculation)
Airport weather information (ATIS, METAR, TAF)
Sigmets



In general, the weather you really need is readily available. An ocean crossing is only a couple of hours. This timeframe is covered by the TAFs. So you shouldn't be too surprised when you don't have all that fancy stuff mentioned above and ask ATC once VHF COM is reestablished or you can receive a VHF VOLMET station.