@ssergutaboselaw – You may need to remove the database tables NextGEN Gallery creates as well as remove any entries in the following WordPress core database tables: wp_options, wp_postmeta, and wp_usermeta … otherwise, using the Plugins functionality of WordPress to delete the files should be fine.
I cannot speak to how your other plugin is maintaining its information and showing “items for NextGen”, you may need to speak with that plugin author for more assistance.
Thanks!
– Cais.
PS: I strongly recommend you have a full verified complete back up of your site before making any modifications to the database.
@ssergutaboselaw You may need to manually delete the three tables in the database of NextGEN, after backup.
Edit: I’m late…
Thank you. I removed all the NextGen database tables, but did not modify the WP tables you mention, photocrafti. I’ll try that.