Every new version uploaded to iTunes Connect needs to have a different build number in order to differentiate the version.

Note: Build number (eg. 1234) is different from Version number (eg. 1.2).

The build number can be automatically increased in these few ways:

Bump in a build script

Create a Run Script in your project Build Phases

#!/bin/bash
bN=$(/usr/libexec/PlistBuddy -c "Print CFBundleVersion" "$INFOPLIST_FILE")
bN=$(expr $bN + 1)
bN=$(printf "%d" $bN)
/usr/libexec/PlistBuddy -c "Set :CFBundleVersion $bN" "$INFOPLIST_FILE"

This will auto increment the build number every time you build the project.

Make use of git commits

If you work in a team, the previous build script will pose an unsyncronized problem.

As an improvement, you can use the total number of commits in your git repository as your build number!

#!/bin/bash
if [ ${CONFIGURATION} == "Release" ]; then
buildNumber=$(git rev-list HEAD | wc -l | tr -d ' ')
/usr/libexec/PlistBuddy -c "Set :CFBundleVersion $buildNumber" "${PROJECT_DIR}/${INFOPLIST_FILE}"
fi;

avgtool

Apple provide a tool to manage the build and version number.

Firstly, setup the project in order to use avgtool.

This is how you use it:

# In your project folder
# Let's check the current build number
agvtool what-version

# To auto increment the build number
agvtool next-version -all

# To set build number to a specify number eg. 1234
agvtool new-version -all 1234

# You can also set VERSION NUMBER eg 1.2
agvtool new-marketing-version 1.2

Using fastlane

fastlane makes use of agvtool to bump the build number.

In any lane of Fastfile, you can add increment_build_number, which will basically call agvtool next-version -all