You will need one of three patches:
iwdpatch106.exe - The v1.06 patch for players without the Heart of Winter expansion.
howpatch141.exe - The v1.41 patch for players with the Heart of Winter expansion. This is not needed if you plan to install the Trails of the Luremaster content in the next file.
HOWTrials.exe - The v1.42 patch for players with the Heart of Winter expansion and includes the free Trials of the Luremaster content.
Patches for the Enhanced Editions will be available through the service where you bought it (Beamdog, Steam, GOG).