Simple instructions to update XDebug on Homestead.

To update XDebug to 2.3.2 (tested) on a Homestead 0.2.5 (tested) Vagrant box, you can use the following commands:

cd ~
wget http://xdebug.org/files/xdebug-2.3.2.tgz
tar -xvzf xdebug-2.3.2.tgz
cd xdebug-2.3.2
phpize
./configure
make
cp modules/xdebug.so /usr/lib/php5/20131226
sudo cp modules/xdebug.so /usr/lib/php5/20131226
sudo nano /etc/php5/cli/php.ini
cd /etc/php5/fpm/conf.d/
sudo nano 20-xdebug.ini 
sudo service php5-fpm restart

Probably this will also work with different versions of XDebug and/or Homestead. Just replace the version number of XDebug to the one you want to use.