LIDAR data is a technical dataset and will need specialist Geographic Information System (GIS) software in order to open it.
If you do not already have GIS software then you may wish to consider using QGIS, which is free to download and there is plenty of documentation available on the internet -https://www.qgis.org/en/site/forusers/download.html
More information can be found in these external links:
- GRASS GIS is built into QGIS and has various tools for working with DEMs https://grass.osgeo.org/documentation/
- Terrain analysis: https://docs.qgis.org/2.8/en/docs/training_manual/rasters/terrain_analysis.html
- 3d terrain visualisation in QGIS: https://www.youtube.com/watch?v=2KrCsbP0kUs
More information including useful links to blogs on how to use LIDAR data can be found here:
If you just wish to view images of the data, you can do this via the “preview on map” feature for each composite layer at https://data.gov.uk/search?q=LIDAR+Composite