You have two choices for installing beta: Option 1 allows you to run the beta alongside the Stable version of Thunderbird, and Option 2 upgrades your existing installation.
Maśo dwě móžnosći, aby betawersiju instalěrował: Móžnosć 1 wam zmóžnja, betawersiju pódla stabilneje wersije Thunderbird wuwjasć, a móžnosć 2 aktualizěrujo wašu eksistěrujucu instalaciju.