[ubuntu] Cleaning up ubuntu insatll

Hiall,

Apologiesif i'm posting it in the wrong forum. I had installed ubuntu 16.04daily builds on my spare laptop to test unity8, elementary osloki(ppa) and few other de's like ciamom, gnome-shell and kde.There might have been others but i don't remember what they were atthe moment.
Ithink i've messed up my ubuntu install a lot. At the moment, it'staking upto 5 minutes to startup and get to lightdm(machine with 8gbram), a further 3 minutes to get to a working desktop and apps likefirefox and chromium are taking too long to open(almost 2 minutes).I've purged all desktop environments with the exception of thedefault unity7 and the unity8-desktop-session-mir package. My laptopis dual AMD graphics and uses the open source raedon graphicsdrivers(though i dont know how to switch between the two AMD graphicscard)

Isthere anyway i can speed up ubuntu? I havent installed manyapplications but in the event speeding up is not possible i'll nukethe system and go for a fresh install though i would like to take abackup of all my installed applications and their data(especiallygames-non steam)
Also,i'm using elementary os freya as a dual boot with ubuntu. Even thatis slow but not as slow as ubuntu.

Inthe event i have to format my hdd, i have a few questions regardingthat:
1.Is there any way i can completely erase everything on it permanently?I mean nothing on the hard drive.. a great big blank
2.Is there anyway i can take backup of my installed applications andtheir data? I havent maintained a separate /home. Everything isunder/
3.Can i replace my laptop hdd with an ssd? If so, how do i do it?should i give it to a computer store and ask them to do it for me?Also, can i transfer data from old hdd to new ssd?

Iplan to use this laptop to lea programming and make software for myown startup with a friend soon.
Thanksin advance for your reply and have a nice day