If you have no experience and no idea how to tinted glasses, you'd better not do it on a really made eyeglasses. Because you are likely ruin the lenses coating on your eyeglasses when tinting your plastic glasses. So, If you want tinted glasses, you can buy a new pair instead. Now, with the development of e-commerce, there are many sites that you can get cheap even free tinted glasses. I have saw firmoo.com offers free glasses. You can have a look. Hope this helps.
Yes. You can get an eyeglass kit which is used to loosen the scews on the glasses and the spray tint that you need to tint your glasses from any optical store. Then use the glasses kit to remove the screws on the glasses to pop out the lenses. Then wipe your lenses clean with a lint-free cloth. Next, shake the spray tint to make them mix up thoroughly. Then Spray the tint over the outer surface of the lenses and let it dry. If you can't do it on your own, you can take your glasses to the optical store where the staff will help you tint your glasses.
You are not advised to tint the eyeglasses by yourself unless you have enough experiences or clear and concrete ideas about tinted glasses. Without decent experiences, your trying tinting would destroy the glasses lenses and the plastic coating. If you really wanna the tinted glasses, there are so many available tinted glasses vendors online such as the Firmoo which has grown into one of the most successful tinted glasses retailers online. It would help you get the better tinted glasses.