You do need a bootable external disk to boot the system, then you can prep your new HD.
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You do need a bootable external disk (or recovery CD/DVD) to boot the system, then you can prep your new HD.
Only the newer models have Internet recovery & you do need internet access from the system (Ethernet ideally). Some older models can get also do internet recovery but you need to update the systems firmware, which doesn't help you now ;-{
Do you have a friend with a Mac? If you do get a USB 16 GB or larger thumb drive with you on your visit. What you'll need to do first is make sure the FAT 32 volume is deleted and you place a GUID partition map onto it using Disk Utility. Then, download if you friend doesn't have a copy yet of the OS installer from the Apple Apps store. Make a copy as the installer file first, then run it to install the OS onto the thumb drive. Once done copy over the OS installer to the drive as you'll need it for your system. Now restart your friends Mac, holding the Option key to get to the boot up manager select your USB drive and make sure your friends Mac starts up if it does you're good to go, shut down your friends Mac and take your USB drive to your Mac and repeat the process on your system. After you finish you can check your firmware following this Apple T/N: [https://support.apple.com/en-us/HT201518|EFI and SMC firmware updates for Intel-based Macs].
You do need a bootable external disk to boot the system, then you can prep your new HD.
Only the newer models have Internet recovery & you do need internet access from the system (Ethernet ideally). Some older models can get also do internet recovery but you need to update the systems firmware, which doesn't help you now ;-{
Do you have a friend with a Mac? If you do get a USB 16 GB or larger thumb drive with you on your visit. What you'll need to do first is make sure the FAT 32 volume is deleted and you place a GUID partition map onto it using Disk Utility. Then, download if you friend doesn't have a copy yet of the OS installer from the Apple Apps store. Make a copy as the installer file first, then run it to install the OS onto the thumb drive. Once done copy over the OS installer to the drive as you'll need it for your system. Now restart your friends Mac, holding the Option key to get to the boot up manager select your USB drive and make sure your friends Mac starts up if it does you're good to go, shut down your friends Mac and take your USB drive to your Mac and repeat the process on your system. After you finish you can check your firmware following this Apple T/N: [https://support.apple.com/en-us/HT201518|EFI and SMC firmware updates for Intel-based Macs].