For uninstall:
- You can just manually delete the plugin folder and then
- Perform the database cleaning, read here:
http://wordpress.org/support/topic/uninstalling-and-reinstalling-1
Many things you can do to minimize the risks, but none can guarantee.
1. Backup your .htaccess and wp-config.php
Both of these files are the very important. In many cases of errors, simply copy/paste from your backups may fix the problems.
2. Backup your database
I do not suggest you to use the database backup feature in this Better WP Security plugin, because many users has reported problems using it. Try these: BackUpWordPress or BackWPup. BackWPup is great if you have external Backup Service like Dropbox.
3. Backup all of your website's files
You can manually compress and save to your local computer, using File Manager (cPanel). Or you may try BackUpWordPress. On BackUpWordPress, you can backup database only, files only, or both using schedule automatic feature or manual.
4. Having good backups, now you don't have to worry when things go wrong. But one important thing you need to remember: don't enable all the features in this Better WP Security plugin. You should enable the features you need one-by-one, after then try it, it everything is working correctly, then you may enable another features (one-by-one of course).
5. These features are very risky, make sure you really understand if you want to enable it:
- Away Mode (may block yourself)
- Content Directory (may cause problem with other plugins)
- Database Backup (may not compatible with some webhosts)
- Database Prefix (may cause problem with other plugins)
- File Change Detection (may not compatible with some webhosts)
- SSL (can cause chaos if you don't know what it is)
7. Those above (no. 6) should be avoid, have great potential to break your website. Here below are less potential:
- Default Banned List (may block some good bots)
- Filter Request Methods (compatible problem with a few plugins)
- Filter Suspicious Query Strings (compatible problem with a few plugins)
- Prevent long URL strings (compatible problem with a few plugins)
8. Consider to move to other webhost
Some nice webhosts allow you to restore backup without a fee. Some also offer free backup feature (on their cPanel). Many of the errors cause by this Better WP Security are 500 internal server errors. This happens because the webhost give user too low available memory.
These additional information if you want read more:
http://wordpress.org/support/topic/500-internal-server-error-199
http://wordpress.org/support/topic/it-seems-very-risky-to-use-this-plugin
Good luck.