ZenCart Upgrade (1.3.5 to current)

We need to upgrade our ZenCart to the lastest. This must include all the latest security patches, etc. We do have some minor user mods that we have implemented to assist with our registration process. Easily found by searching for 2 keywords. Also would would like the ZenCart pages to look more like our new web site. Any ideas you have to enhance either ZenCart or our site to be more SEO friendly or more geared to our business will give you a bonus. The ZenCart system must be as hacker proof as possible. (we have a hacker plishing from our SMTP account now). Must not use Admin, or zencart, etc. I am sure you know what I mean. This is somewhat of a rush.