The order of the visible tiers in the timeline and interlinear viewer can be altered. To achieve this, right click in the tier name panel and select the sub menu Sort Tiers. Then choose one of the following options:

Table 4.5. Sort tier options

Unsorted: no specific order.
Sort by Hierarchy: display a tree with the hierarchical structure of the tiers
Sort by Linguistic Type: group tiers by their linguistic type
Sort by Participant: group tiers with annotations of a single participant

It also possibly to sort the tiers alphabetically along with the anyone of the sorting options before. To do this, right click on the tier name panel and select Sort Tiers > Sort Alphabetically.