In my native language, the English word "develop" is translated to: the process to make something/somebody large/strong/big, and etc. for example: economic development.
Develop has many different meanings in English. Mostly it could mean to bring to a more advanced state, cause to grow or expand, to elaborate or expand in detail, or to bring into being. There are many more specific meanings depending on domain.
Upgrade has a relatively more narrow definition, and means to improve something that's old or outdated, or to raise in value or esteem.
You could possibly find one where upgrade could be used instead develop, but it would be difficult, and it would be in only one specific meaning. Develop has the sense of an ongoing process, upgrade is discrete. You upgrade something from one stage to another. You develop something from a less advanced to a more advanced state in a gradual process.
To use your example, an economic upgrade would be a something (very specific) that happened to the economy that could be precisely measured as better. An economic development would be something added to the economy that is new, or depending on context, you could be speaking of the economy made generally better through several changes.
Another way of thinking of the difference, when you "upgrade" something you are literally or figuratively replacing something with something improved. When you "develop" something, you are changing something (usually improving it), or creating something new from scratch (not replacing anything.)
It's interesting when I was searching for usage, one example I found of the phrase "economic upgrade" happens to be an obvious translation, so "economic development" would have been better…
The words develop and upgrade are used quite differently.
Take for example computers. If you work to improve the program then you develop the software, while the end-user then upgrades his system to the new version.