You should install these patch one by one. Here is how to install patch.
You should go to
app/etc/applied.patches.list and check which one is installed.
I would suggest you to install all of the available patches, since they fix loads of bugs.
By accessing magento my account (recommended) or in below link you will find all the available patches:
Remember, each patch depends upon another, so you must apply those patches from first to last.
Obviously, before applying these patches to live site, you should test them in testing site to make sure everything is ok.
When downloading patch, make sure you choose the right version of your magento.
Some of the issue you may come across:
Checking if patch can be applied/reverted successfully...
ERROR: Patch can't be applied/reverted successfully.
- Why does PATCH_SUPEE-6788 appear to have no effect on a 18.104.22.168 installation?
- Security Patch SUPEE-7405 - possible problems?
- Magento Patch 7405 v1.1 update error