How to know the process ID that lock apt-get upgrade [ or any synaptic download process] and then stop that process ?

to know the process id issue following command:

ps -ec | grep apt

then look for pid and issue command:

kill -9 <pid>

ps -ef | grep -i jockey

ps -ef | grep -i python

you will get the processes but with the jockey is the one which locks the apt-get you just have to

kill that pid with kill command

You can also use

ps ax

in place of

ps ec

.