How do I increase the tech level of my industry?

In my experience so far, the most important factor in increasing industrial tech is placing a community college or university in your city. You can also accelerate the process of converting your industries to high tech by placing this near your industry. It will immediately boost their happiness (you will see green smiling faces pop up), and they will begin to develop very soon.

For example, let me give you a scenario from my play time last night. I had a decent size city going (50,000 pop), with demand through the roof for residential and industrial zoning. This city is currently the only one in the region, so there were no outside factors influencing my city education level, or any sims coming from other cities for jobs. I had a large industrial sector comprised completely of low tech dirty industry, even with a well funded grade and high school operating.

Having read the tool tip for the community college, I decided to plop it on the edge of where my industrial zones met my medium to low income housing zones, as the tooltip indicated it would help boost industry and be a place for mid income sims to receive college training.

The moment, and I mean literally the moment, that my community college staffed itself and opened its first classes... every factory within 4 blocks began upgrading itself to mid-tech industry. In fact, my income dipped about $4000 while all the factories upgraded at the same time.

So, in conclusion, if you want high-tech jobs, you need not only educated sims, but college educated sims, preferably university educated for the highest tech level.

Look at the Tech Level map overlay, which will tell you the progress your industry is gaining in tech. It should be green. If it's not green, put more education in your city, or you can acutely effect tech by putting colleges adjacent or very close to your industry. I slowly increased to Tech III by using only a Grade School and a City College.