I wish to update the software as the version 1.9.5 takes a long time to syncronize when booting up.
i may be wrong but upgrading has nothing to do with the time it takes to load the wallet (won't change it) it takes longer because your mywallet file size is getting big.
Thanks
what do you mean by "leave open" you mean keep the old version? if so then you can't because electrum is being installed in the same directory as the old version and will replace the old electrum files.
but also since you are upgrading from 1.x to 2.x your mywallet file will also be upgraded.
read more about it here: http://docs.electrum.org/en/latest/faq.html#how-to-upgrade-electrum
so be careful before upgrading, make a backup from your wallet file and also your seed before upgrading.