Look for a 'YSlow' plugin for your chosen browser (they exist for Chrome and Firefox), which can help you to identify things that are causing your site to appear slow.
After that, then I would look at CDN, and then I would look at database optimisation (many people just don't "get" indexes, and don't understand how much of a difference they can make), and finally code optimisation.
A lot of questions like yours have already been asked with hundreds of great responses. Just spend an hour searching around for database indexing, using a CDN, and writing better sql queries and you'll have pages and pages of invaluable information at your fingertips.
Ultimately, though, you should look at trying to do as much as you can yourself. The better you understand your system, the better you can run your company.
Still, CDN and database optimisation isn't the first place to start. As I mentioned, look at YSlow, which should give you a few places to work on for optimising your sites.
As mentioned by someone else, depending on the technology your sites are running on, there may also be plugins/tools available to speed things up with little to no real effort.