To extend your lease, you must agree and pay a reasonable 'premium' to the Landlord who owns the freehold of the building. There is statutory guidance on how this premium should be calculated and it is possible for you to negotiate the premium and terms of a lease extension directly with your Landlord (a non-statutory lease extension), but there is no obligation on their part to agree the premium and no option to compel them to grant an extension. The most reliable route is therefore to seek a statutory lease extension.
If you extend your lease for 90 years via the statutory process, you stop becoming liable to pay ground rent. This can help to offset the costs you incur in extending the lease and is a further benefit that is guaranteed by using the statutory route. The flowchart below outlines the process of the statutory process. As you will see the statutory process also has certain key fixed time limits which ensure the process cannot be blocked indefinitely.