The following explains how to use/improve/transmute runes. First of all there are two ways to improve them:
2. Merge 5x runes with same name and with same tier (level) to create 1x rune with same name but with 1 tier higher.
All the possible transmutations are split in ranks. There are 8 ranks:
There are some runes, that can't be crafted. For example: Block Rune. This rune can’t be crafted using Tier 1 runes but instead, can be done using Tier 10 Runes. This also will affect other higher ranked runes which use block in their process like Hatred. You can’t create a Hatred Tier 1 using Block I and Aggression I but you can do using Tier 10 ones.
And also there are runes that are disabled in the game and this process don’t allow you to complete them. Loot Rune is one.