I have already bought Gardenheaven theme and downleaded to my computer hard disk. How can I install the wordpress purchased theme
Hello 
Within the zipped files you should find instructions on how to upload the theme to WordPress as well as how to customize it to your needs.
Thanks!
Dear Sirs,
After getting the theme i worked on in two days to install into my
subdomain landscape.pegacons.com. Unfortunatelt I understood that I must
have a huge knowledge to use this application and establish and control the
site permanently. Today I am also cancelling my wordpress hosting from
ihs.com hosting server provider. I have no sufficent experience to use the
purchaed theme. I am demanging the returning of my payment from Envato
company ans asking to begin the prosedures to cancelling my purchased theme
and return back my payment.
Kind Regards,
Aydogan Ortaç
Refund information is here https://help.market.envato.com/hc/en-us/articles/202821460-Can-I-Get-A-Refund- although please be aware that not having technical skills to use an item is not usually grounds for a refund.