Well this is something that magic can actually help with but as I'm sure you can appreciate its a bit more complex than bibbity bobbidy boop and now you're happy. The first issue is to identify exactly what it is that's causing your unhappiness and come up with a way to solve it. Often negative energy can make people unhappy and cleansing yourself could help considerably but as you chose to use the word grieve I'm assuming, and perhaps falsely, that you're unhappy because you've lost someone which I'm sorry for if you have, but wounds like this take time to heal and there are things you can do to help you along the road but it is a long journey. Magic isn't a one stop cure and it won't make all the pain disappear but it might help put those feelings at ease.
Before you could cast the spell however you'd need to become familiar with the basics, which actually covers most of what you'd have to do anyway so I personally suggest you start looking at them.
Clearing your chakras and keeping them open and your body in balance can help bring down inner turmoil.
However, for the majority of getting happier, you need to grab hold of your life. Why are you sad? You need to find the reasons and cut them from your life or fix them.
may recommendation is find out what is cosing you sadness than right them down on a piece of paper than burn the paper that has the name and is infused with all the sadness that you have and let the power of fire free you from the sadness. so lite a fire with some type of wood in a safe place and burn the sadness away in the fire.
your right, we never stop longing for the ones we lost, we never stop grieving. but i dont know, this just may not be something magic should fix. i dont like grief anymore than you, but we grieve for a reason, and eventually the hurt does lessen, the pain does recede. and you find yourself smiling when you think you should be crying.