The exact length of time you can renew a domain for depends on the domain itself, as different TLDs (Top-Level Domains) have different rules about renewal lengths.
Broadly speaking, however, most gTLDs (Generic Top-Level Domains, e.g. .com, .org, etc.) can be registered for up to ten years at a time (ie if you have one year before your domain expires, you can only add nine years worth of renewal).
ccTLDs (Country code Top-Level Domains, e.g. .uk, .fr, .tv) can vary a lot however and if you want to renew one for longer than the standard 1-2 years it'd be best to get in touch so our domains team can go over your options with you.