You need to have iFile installed for this, MEANING ONLY JAILBROKEN DEVICES CAN DO THIS! This is mainly for convenience.
1. Open iFile to /var/mobile/Applications/Junk Jack.
2. Open JunkJack.app.
3. Press the "Edit" button in the top right corner, tap on all the texture files.
4. Tap the Clipboard button in the bottom right. When asked tap "Cut".
5. Go back to /var/mobile/Applications/Junk Jack.
6. Go to Documents. This is where the worlds are stored.
7. Tap the Clipboard button in the bottom right. When asked tap "Paste".
8. Press the "Edit" button in the top right corner, tap on all the texture files.
9. Tap the Clipboard button in the bottom right. When asked tap "Copy".
10. Go back to /var/mobile/Applications/Junk Jack/JunkJack.app.
11. Tap the Clipboard button in the bottom right. When asked tap "Create Link".
12. Plug device in and open iTunes, go to your device on the left hand column, then click Apps in the top bar-thing.
13. Scroll down and go to Junk Jack, the texture files should be there. Replace them with the desired texture pack.
14. On your iThing open multitasking, double tap home, and close JJ.
15. Open JJ.
16. ???
17. Profit!
-Killerofsheep
1. Open iFile to /var/mobile/Applications/Junk Jack.
2. Open JunkJack.app.
3. Press the "Edit" button in the top right corner, tap on all the texture files.
4. Tap the Clipboard button in the bottom right. When asked tap "Cut".
5. Go back to /var/mobile/Applications/Junk Jack.
6. Go to Documents. This is where the worlds are stored.
7. Tap the Clipboard button in the bottom right. When asked tap "Paste".
8. Press the "Edit" button in the top right corner, tap on all the texture files.
9. Tap the Clipboard button in the bottom right. When asked tap "Copy".
10. Go back to /var/mobile/Applications/Junk Jack/JunkJack.app.
11. Tap the Clipboard button in the bottom right. When asked tap "Create Link".
12. Plug device in and open iTunes, go to your device on the left hand column, then click Apps in the top bar-thing.
13. Scroll down and go to Junk Jack, the texture files should be there. Replace them with the desired texture pack.
14. On your iThing open multitasking, double tap home, and close JJ.
15. Open JJ.
16. ???
17. Profit!
-Killerofsheep