Digital technologies have increased worldwide in the last years. In addition, the pandemic has strengthened digital technologies' roles in education, requiring twenty-first-century skills, such as digital competence, and indicating a new normal. Digitalisation in education creates opportunities that could lead to positive effects if digital technologies are applied correctly. However, applying digital technologies can incorrectly trigger a negative development -- for example, increasing workload due to nonfriendly user interfaces in software and reducing the motivation to apply digital technologies in education due to a lack of digital competence. Teachers require access to digital technologies and digital competence related to educational issues that influence equality within and among K-12 schools, thus making school leaders' roles crucial in digitalising education. Three group interviews and a survey were used to collect the data in a network of three municipalities in Sweden. The data have been categorised and analysed with thematic analysis. The results show that school leaders describe the digitalisation process in the form of digital competence for teachers, access to hardware and software, and a shared culture. School leaders explain that clear guidelines, collaboration between teachers, and enough time enable digitalisation in education. However, the lack of support and the lack of resources constrain digitalisation in education. At the same time, school leaders do not often discuss their own digital competence. The school leaders' roles in the digitalisation of K-12 schools are important, requiring digital competence for leading the digitalisation process.