Because Tally Solutions discontinued support for version 4.5 decades ago, there is no official "download" link on their current website.
If you are downloading it to access old files, Tally Solutions provides a Migration Guide to help you move Tally 4.5 data into Tally.ERP 9 or TallyPrime. Download Tally 4.5
Modern CPU is too fast for the timing loops in Tally 4.5. Fix: In DOSBox, reduce CPU cycles. Press Ctrl + F11 to slow down the emulation. Because Tally Solutions discontinued support for version 4