can erase partition without losing data

You can delete and merge a partition that immediately follows the one you want to keep.

You cannot delete and merge a partition without losing the data. Copy it to another drive or backup before trying to merge the partitions.

Partition a physical disk in Disk Utility on Mac - Apple Support

I would actually advise you to go a step further and make sure to have the data from all three partitions backed up before doing anything else. Whenever you manipulate partitions you risk losing everything on the drive. If something goes wrong be prepared on how you will erase the drive and reinstall macOS or restore from a backup since you may not be able to boot to the internal drive if something goes wrong.