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.
Maće dwě móžnosći, zo byšće betawersiju instalował: Móžnosć 1 wam zmóžnja, betawersiju pódla stabilneje wersije Thunderbird wuwjesć, a móžnosć 2 aktualizuje wašu eksistowacu instalaciju.