Android keystore password change

I would like to change the password I use in my keystore for an android app that is already available in google play and I would like to know some things before I do it:

1) If I change the keystore password, could I continue using the same keystore for my uploaded app without any issue (I need to do this, this is why I ask)

2) Does changing my alias password has the same consequences?

3) How should I use keytool?

If you are using the same keystore for signing your application before pushing it to the play store, it should be fine.
Changing Keystore's password or alias password doesn't affect the way it is used to generate the signed apk.

In order to update the password using keytool:

1. Open cmd prompt
2. Browse to the location of the keytool / set the location of keytool in the path variable under the system variables and directly go to step 3
3. Run the following command:
   keytool -keypass "previous password" -new "new password" -keystore "keystore location"

Security Note
As mentioned in vlz's comment below.
You should not include your password in the command because it'll be written to your command history (~/.bash_history).
Instead, you can use the below command (safely prompt for a password):
keytool -storepasswd -keystore "keystore location"

Recovery plan
Make sure to backup your keystore file first.