const SiteClient = require('datocms-client').SiteClient;
const client = new SiteClient('YOUR-API-TOKEN');
const siteInvitationId = '312';
client.siteInvitation.update(siteInvitationId, {
  role: '34'
})
.then((siteInvitation) => {
  console.log(siteInvitation);
})
.catch((error) => {
  console.error(error);
});

> node example.js
{
  "id": "312",
  "email": "mark.smith@example.com",
  "role": "34"
}