There are 2 methods that you can try:
1. You can use a renamer software that will automatically rename all your files starting with 00 to 1, 2, 3, 4... I'm currently using Advanced Renamer which is free and good!
2. You can also pack all of them to... a spritesheet using Aseprite or any spritesheet packer software, then just tell the plugin how many columns and rows the file has and let it handle the rest.
If you're still struggling with both of those methods then you can tell me again and I'll make an update to the plugin.