the standover height on my bike is a but tall. I can touch the ground, but I touch the top tube as well. Any ideas?

The bike is too big for you

At 158cm (5'2" for our American viewers), you really should be on a 50cm frame size (or 49 - 51cm depending on brand). That being said, you don't necessarily have to move to a smaller size. You say you can comfortably ride the bike at it's current size, but getting off is challenging. It might help to review your dismount technique. The proper (and easy) way to get off a bike follows these steps:

1. slow down almost to a stop
2. take one foot off the pedal
3. stop and place that foot on the ground
4. shift your weight onto that foot
5. swing your other leg backwards and over the saddle
6. put both feet on the ground.

You now should be standing next to your bike holding the handlebars.

If this solves your problem dismounting, and you continue to ride without discomfort, then you're fine on the bike. If not, you may want to consider getting a bike that fits you a bit better.