I want to play minecraft with a colleague of mine using Technic Launcher. If I want to install a certain modpack, it loads up to 10% and then goes back to 0%. Can i change that
There could be several reasons. The modpack may be too big and your internet speed too slow.
Perhaps it is also due to the Technic Launcher itself. In this case, delete all data in the .technic folder and reinstall the Technic Launcher.
Otherwise, possibly reinstall Java.