Whenever you update your review, there must be roughly a 10% change in the text in order for any change to appear in your user info.
But my review is old, I don't use that ISP anymore ...
You cannot delete your old review(s), but you can review your new ISP by finding it on the ISP List (front page of DSLR), going to the page for that service provider and clicking on "submit a review." Please note that in order for your new ISP to replace your old one it must be the last one edited by you. In other words, don't review your new ISP, then edit your old one.
When I click write a review it says that I already have a review. I try to update it, but I can't change my ISP.
First, find the ISP. Then, click into its listing, click into user reviews and, finally, click into "write a review." It will take a day or two to update. However, if you go to your forum preferences (where you have your zip code, etc), and re-save without changing anything, it will appear in about 20 minutes.