how did you do the thing with more than one sidebar?
Go to THIS WEBSITE and copy the first part of the code (there are two of these boxes and you need the first one now). You then go to edit your theme (edit HTML) and paste the code below (it has to be above the meta tags).
100.jpg 200.jpg etc with the urls of the images you want
it should look like this then:
theImages[1] = 'https://24.media.tumblr.com/2457e4eff8f3b35ef462aacd4bca7a86/tumblr_n4y5whBK9F1rh1v8lo6_250.gif'
theImages[2] = 'https://24.media.tumblr.com/81931315781ec28c939e083a741b8376/tumblr_n4y5whBK9F1rh1v8lo3_250.gif'
Then you need to copy the second part of the code and find the source of your sidebar image in the HTML. It looks different for every theme but mine looked like this:
It's most likely in the . What you need to do now is replace with the code from the second box. I made the mistake at first that I only replaced the thing between the { } and then I got really frustrated haha.
I hope you can follow what I tried to explain