Either Way...
You may be able to work out in the morning...you may not but give a try. However if you are going to workout in the morning, make sure you get something to eat before you go running- Your body needs that energy.
You may be tired at night...so wait until later on that night- That may work.
If you're tired after work...that's typical but you can try to do a little at a time. Most of it is because your body isn't used to doing some form of activity after work, you used to and you got lazy, you are not eating properly, you are not drinking enough of your fluids...all these things could be affecting your routine. You may not even get enough or too much sleep.
What ever you do, start in small steps otherwise it will be too difficult and you'll give up.