hi, if you are looking for a quick switch - does that mean you are just changing the image, keeping the original dimesions ? just upload a new image into your app_themes/YOURTHEME/images folder - use the default name to overwrite the existing ( think its logo.gif )
contact me if you need assistance
ssl - you should be able to buy this through your hosting company (you might find a cheaper one elsewhere, but check how much your hosting company charges for installing 3rd party ssl's )
they will instal it for you - normally you will only have to set up an emailaccount on your domain to handle the ssl