If you do not have a disc player, you can buy the digital 4K version.
If you want to demo the 4K quality to friends or test your TV, skip to these timestamps: frozen 1 4k
Sources for further review:
The 4K release features HDR (and often Dolby Vision). This is arguably more important than the resolution for this specific film. If you do not have a disc player,
You can buy Frozen 1 4K on Amazon Prime Video, Apple TV, or Vudu, but beware of compression. Streaming 4K caps out at roughly 25 Mbps. The physical 4K Blu-ray disc runs at 60–80 Mbps. For a film filled with fast-moving snowflakes and wide landscape shots, the physical disc avoids the "banding" (visible color stripes in the sky) that plagues the streaming version. Sources for further review: