If it's Land Registry property (you have a folio number), the front page will tell you the details of the lease. If not, you will have to contact your solicitor.
If you want to purchase the Ground Rents, you can track down the landlord, but if you can't there is an arbitration procedure in Ground Rents which will set a price which is paid into the Land Registry. If the landlord ever does turn up s/he gets the money you paid in.
It,s relatively straightforward, and if you have a vesting certificate you can then sell both the freehold and leasehold interests to the purchaser.