I would recommend the 64 bit OS. That's the direction everything is moving. It will give you full compatibility with both 32bit and 64bit software. It may use a bit more memory, but the potentials to upgrade in the future and get better speeds are worth it.
As long as this is the correct laptop https/support.lenovo.com/ca/en/documents/migr-75358, it's true that you will be able to access more than 3Gb of memory with 64bit windows.
However, unless you decide on adding new/used ram to replace what you have (keep with the same spec of memory, 8Gb max), you won't see any significant difference between 32bit/64bit. because most programs outside of photo and video editing won't take advantage.
If its this one http/shop.lenovo.com/ae/en/laptops/lenovo/e-series/e40/ than you should have been using the 64bit version from the get-go.
The Laptop details show that It can use Up to Intel® Core™ i7 processor. That means that the processor should support 64bit OS. There are clear benefits of using 64bit OS.
1. More usable RAM
2. Better OS performance
1. Need to find 64bit versions of Drivers and Software, to utilize complete benefits. Some softwares do not have 64bit versions (like Symantec Antivirus)