If you are a site webmaster and you would like to delete all the DNA matches, you should turn off the DNA Matching option under the privacy settings on your family site, following these steps:
1. Log in to MyHeritage.
2. Click on your name in the upper-right corner of the screen and select “My Privacy”.
3. Under “DNA preferences” you will be able to select the DNA kit for which you wish to customize the preferences and see “Enable DNA Matching”. Here you can apply privacy settings according to your preferences.
4. If you uncheck the box 'Enable DNA Matching on MyHeritage', all the DNA matches found for you or for your family members will be deleted.
If you turn the ‘DNA Matching’ feature back, then the matches will be recalculated.
If you would like to delete the DNA matches for someone specific, you need to delete the DNA file you had uploaded for this person. This also applies to site members who had uploaded DNA data files for themselves in the past. Read here for more details: How can I delete my DNA data?