Do I have to change my wifi password regularly?
Answer first
Not regularly. Once, properly, is enough, as long as the password is long and is not the default the device came with.
Change the password if it is a shared default, it has leaked or somebody unauthorised knows it. Otherwise, a calendar-based change is unnecessary.
What matters more is that you are not still on a default password. A password printed on one particular unit’s label is reasonable. One that is the same on every unit of the model is not a password at all.
The other point that gets forgotten is the router’s admin password. That one opens the settings, and in plenty of homes it is still the one the factory set.
Length beats special characters. Four words in a row are easy to type and hard to guess.