Where can I edit three images at front page (Rooms, Services, Activities)?

Those 3 images with titles at Front Page are child pages of your Home Page:

- Activities
- Hotel Rooms
- Hotel Services

In order to change image you need to go to edit one of those pages and change its Featured Image.

In case you want to add more images you should Add new page> add title and featured image > define Home Page as Parent one. Then Publish and check the Front Page preview.