Hi, the first few times most people try an enema it can be a bit "clumsy", difficult to accept more than a pint or two, and may be somewhat uncomfortable. Nevertheless, before too long, as you figure what works out best regarding position, height of the bag, best place to take take the enema etc, things get easier, it's more comfortable, and results are better.
As far as temperature, it should be about 103 degrees F at preparation time. Rather than guess, a bath thermometer is highly recommended. If you have a baby bath thermometer, that works great.
Here's a few links with some more information that I hope you find helpful, followed by a position that I find quite comfortable, especially when taking an enema while lying in bed.