You should be able to check with your brokerage about whether or not you currently hold Class A shares directly. It should be on your account statement somewhere, or there might be a list of a CUSIP for the shares, which is often unique per share class.
From a brief skim, looks like there are Class A and Class B shares outstanding currently. 100% of the Class B shares are held by a single person - which presumably isn't you. Therefore, most likely, if you hold direct shares, you hold Class A shares.
The offering provides that each share is entitled to buy a new Class A share at $33.52. If you don't buy that new share, you will be diluted because someone else will buy that share in your place. If you have 100 Class A shares now, you can buy 100 more class A shares.
Usually you can exercise your rights to buy the shares through the broker where you hold your current class A shares. Typically your brokerage would send you the notice and there would be more detailed information about how you can exercise your rights to buy more.
For any shares of DISH held through an index fund, you don't own those directly - the index fund owns those shares. The index fund gets to decide whether or not to buy additional shares - you don't get to decide what the index fund chooses.
