You may have several options, but which ones are available depends entirely on the event organiser. Some offer all of them, some offer none, and some charge a fee for using them.
Seeing what is available to you
Log in to your Race Space account at race-space.com, opening the main menu and selecting Register/Login if you are not already signed in.
Select My Entries. Every entry you have bought is listed.
Find the entry and select Entry Actions. On a narrow screen you may need to scroll to the right of the page to see it.
Whatever options the organiser has enabled appear in that menu. If an option is not there, the organiser has not made it available for this event, and no amount of searching elsewhere will find it.
The three possibilities
A refund returns your money, in full or in part, according to the organiser's terms.
Exchanging your entry for a credit swaps the entry for credit you can spend on another event by the same organiser, valid for 12 months from the date you exchange your entry.
If you bought XCover protection at checkout and cannot attend for one of the covered reasons, you claim through XCover directly rather than through Race Space or the organiser.
Each has its own article explaining how it works and what the conditions are.