Difference between 4k and BlueRay?

A few things:

There is no E in Blu-ray Disc.

Blu-ray doesn't have a set resolution, but most commercially produced discs are currently 1920x1080 AKA 1080p, but many have SD (720x480) extras.

4K (4096x2160) is not 4x the resolution of 1080p, it is 2x the resolution each way of 2K (2048x1080) for 4x the pixel count.

The home format isn't called 4k, it is called UHD or Ultra HD and is 3840x2160, but it isn't just about resolution. It is also about wider color gamut, more color bit depth, higher dynamic brightness range, Etc.

This is a problem because there are already TVs labled as UHD when they only have the resolution and not the rest, and since this is all hardware related and can't be fixed in firmware these TVs were already obsolete before they even went on sale to the public.

The updated physical media spec is called (not surprisingly) Ultra HD Blu-ray Disc, and yes it requires a new player and is the reason that I haven't replaced my current 3D Blu-ray Disc player that no longer reads DVD or CD.

BluRay is a disk format that can hold HDTV video (1080 resolution max).

The UHD or 4K does not yet have a disk format although I have heard the spec's have been created.