How can I check github releases in c#?

Something like this.

void UpdateCheck()
{
    if (GithubApi.GetCurrentRelease().Version > CurrentVersion)
}

How can I do this?

I found some API, https://github.com/octokit/octokit.net

but I can't find this function.

Solution

Using Octokit.net you should be able to get started using this example from the documentation:

Get All

To retrieve all releases for a repository:

var releases = client.Release.GetAll("octokit", "octokit.net");
var latest = releases[0];
Console.WriteLine(
    "The latest release is tagged at {0} and is named {1}", 
    latest.TagName, 
    latest.Name);

Alternatively, you could use the API directly:

List releases for a repository

Information about published releases are available to everyone. Only users with push access will receive listings for draft releases.
GET /repos/:owner/:repo/releases