Windows 10 is a free upgrade at the moment, and you can get 64 bit Windows 10 even if you have an old 32 bit Windows OS.
For example, I had Windows 7 Pro 32 bit. Upgrading to Windows 10 32 bit gave me a license code for Windows 10 - which then allowed me to do a fresh install of Windows 10 Pro 64 bit on top of it, retaining the license.
The pain of switching from 32 to 64 is that you must reinstall all software, it's not an upgrade path that keeps your current system and converts it. That can be an opportunity to clean things up, but be sure to deactivate any existing software licenses that require in-product deactivation first. (Office 365, for example, can be deactivated from the Microsoft web site, then re-activated. Artlantis must be de-activated from within the product in contrast.)
In my case, I upgraded virtual machines - so now have the upgraded 32 bit Windows 10 machine with all previously existing software should I need it, and then the copy of it that I upgraded to 64 bit Win 10 and use daily.
A little time-consuming, but it's free.
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB