1. Make sure you have researched "Colony Cluster Level 1/2/3" (not required for collectives)
2. Make sure you have the required number of colonies for clustering
3. Go to "Projects" under the section "Economy" on the left side of the screen
4. Select "Colony Upgrade"
5. Select the type of clustering you wish to use
6. Select the type of mineral this cluster will have from the list of options
7. Click "Confirm"