How do I install 8 years old Photoshop?

hi to everyone

i recently bought a new laptop and managed to set up a few things which caused it to run slowly so i reset it back to factory settings in the process losing 'photoshop'. 

i then tried to reset 'photoshop' and received the trial version for one month after which time i have to pay and have been quoted 86GBP per month.

i originally bought 'photoshop' about eight years ago for £79 approx and have never paid a monthly fee in the eight years since.

can someone please explain why i need to pay a monthly fee now. im not using it for a business. im retired and purely using it to help with my non profit making website

could someone please explain