Viber is one of the top 3 internet messaging applications which lets you have free texts, audio calls and video calls. Stickers are used to bring emotions to text messages and in case you've downloaded so many stickers and are running out of memory, here is the way to delete stickers on Viber for Android:
(Note that, if you don't care about losing your messaging history (especially Viber groups), the best way to get rid of the entire stickers is to uninstall and re-install the Viber application itself)
How to delete stickers on Viber for Android:
1. Make sure you have a File Manager application installed on your device, which enables you to view hidden files (we used ES File Explorer File Manager)
2. Open Viber, tap the 3-line icon on the bottom right, and then open the Sticker Market option
3. Tap the Gear icon on the top right, and there you should see the list of your downloaded stickers
4. Now, mark the Stickers you'd like to have, and unmark the ones you'd like to delete from your device
5. Open your File Manager, and make sure the "Show Hidden Files" option is marked. (On the ES Explorer, you just need to swipe right from the left edge, tap the Tools option and enable "Show hidden files")
6. Go to this path: /Sdcard/Viber/media
7. There you should see a hidden folder named: .stickers
8. We recommend you to have a backup from .stickers folder before going to the next step
9. Open the .stickers folder and delete the entire Folders (Tap and hold on one folder to enable multi-select mode, and then use the Delete button)
10. Now, open Viber again, start a new conversation and try adding a sticker. As you can see, the already available stickers are about to be downloaded again (The ones you marked at step 4), and the rest have been deleted and you've gained some free memory.
11. Enjoy!