I need to change the type of an existing column/question, for example, from text box to number or drop-down. How can I do this? Thanks in advance!
On a new project, just delete the old questions and replace them.
On existing projects (with entries already collected), you cannot do it. If you remove a question, you will lose the answers to that question.
You could, however, download a backup of your data and then manually fill the missing data in, either in Epicollect5 or the exported csv file.
The main reason changing question type on the fly while preserving existing data is not implemented is because it could lead to data inconsistency and invalid entries. For example, if you start with a TEXT question, collect some entries and later change that question to a NUMERIC one, suddenly all your previous TEXT answers containing letters will become invalid since a NUMERIC question type does not allow letters, only digits.