If what you entered as a tag is correct, and you use Jira software, then SLAs do not exist in them. They only exist on Service Management Projects. Having said that, if you are on a JSM project, then go to project settings > SLA. Then see their configuration there.
If not you are on a software project and you see some kind of SLA then you could either go to project settings > apps and check if any app configuration is visible there, OR you have to go to cog > apps and find from the left menu the SLA app (you have to know how it's called). And from there you could edit the SLA.