Lightroom can export JPEGs from RAW files, but the answers provided do not point to any built-in feature or plugin that safely “replaces” RAW files in-place while preserving the catalog relationship. In practice, the better options are:

• If storage is the issue while traveling, shoot RAW+JPEG, import/use the JPEGs on the road, and keep the RAWs on the card until you get home.
• Back home, you can import the RAWs and sync metadata/develop settings from the JPEGs if needed.
• If you want smaller originals than proprietary RAW, consider converting to DNG instead of JPEG.
• If possible, use external storage and backups rather than deleting originals.

Several responders note that deleting RAW after export defeats much of the benefit of shooting RAW in the first place. JPEGs are fine as final output, but they don’t preserve the same editing flexibility as RAW. If long-term space matters more than re-editing latitude, exporting JPEGs and manually removing RAWs is a workflow choice—but it’s not presented here as a simple Lightroom one-click replacement feature.