Unable to change table prefix from wp_ despite multiple attempts

I have been trying to do this ever since I installed my blog but I have never been able to. The guys at my hosting company (blue host) have not been very helpful in assisting me. I am fairly technically but doing this manually is above my head. I am currently running 3.2.1 (MYSQL Version : 5.1.56-community-log, PHP Version : 5.2.17). Other than this problem my blog has been running virtually problem free except for one other minor bug mentioned here.

The really slick new “WP-Security Admin tools by WebsiteDefender” seems to have an an automated tool for changing this but when I tried it crashed my blog horribly. The whole thing reverted back to a new blog installation. Thankfully I backed up the database and restoring the database and then resetting the permalinks fixed it. I needed the help of support and they told me something that wasnt really clear – that changing the tables was successful but it made a second copy or something. In any event it didn’t wipe-out the database because it was still 20+ megs.

The other strange thing is that “WP-Security Admin tools by WebsiteDefender” says:

“The database user you’re using with WordPress must have ALTER rights. (No)”

The user has full rights. I have checked and double checked. I suppose it would not have been able to crash the blog if it didn’t have alter rights but this message is always displayed.

Can anyone help explain how to change the table prefix without crashing the blog? If I do change this is this something I will have to do again and again everytime I upgrade the wordpress versoin and/or theme version (I guess not the theme but maybe wordpress)?

Thank you.