Ask anybody if they'd rather catch a movie or read an IT manual and the movie will win every time. So, with that in mind, here is what I suggest you do if you really do get tired of studying.
1. Remind yourself why you started in the first place.
Do you want to improve your life situation, find a more challenging role, get paid what you're worth or just prove to yourself that you can actually stick to a goal and see it through?
I like to stick images of my goals and outcomes right at the side of my computer monitor.
2. Ask yourself if you are overworked or just lazy.
There is a big difference between exhaustion and laziness. If you have worked a long shift, driven two hours home in busy traffic, cooked dinner for the kids and now have to study for three hours then you will be tired. If you've spend the day posting on Twitter and eating then you might need to give yourself a kick up the butt.
3. Walk and breathe.
Did you know people don't move or breathe enough? They sit in the same chair for hours and take little gasps of air. No wonder they feel like crap.
Every hour you should be moving around and filling your lungs with some deep breaths of (preferably) fresh air. It will recharge your body and oxygenate brain.
4. Study something different.
There is nothing wrong with coming back to a difficult subject later. I do it with guitar music all the time. If I can't get it under my fingers I'll play something easy. The hard song isn't going anywhere.
5. Study differently.
If you are reading the same paragraph over and over again and it isn't' sticking then you might be doing it all wrong for the way your brain likes to learn.
Do a hands on exercise instead, watch a video, do an exam, listen to an audiobook or podcast. You can read forum questions on the subject or even documentation or white papers from the vendor.
6. Take a break.
Some people beat themselves up if they don't hit their target goal.
What is the point of that? We all have off days. Some of us can absorb information quickly but the rest of us need to pace ourselves and let things sink in over time. Unless it's exam day tomorrow you can always adjust your study plan back by one day. Spend the time away from studying doing something you ejoy.