Hello !
To remove the spring you do not need any special compression tool. This tool is only needed to reassemble.
Remove the head from the bike and put it on the bench, piston side down on a rag (the purpose of the rag is to fill the combustion chamber and retain the valve).
Get a tube wrench bigger than the keepers diameter but smaller than the retainer. Get a middle size hammer.
Put the tube wrench on the retainer, and strike it with the hammer, a firm strike while retainer the wrench with one hand.
The strike will press the spring down freeing the keepers which will stay in the tube wrench.
If you hold the wrench with "some force", the spring and retainer won't jump.
It's easier to do than to explain.
This way, you will be able to check what's wrong, broken, and order the parts you need.
Definitely you need a new set of gaskets : push rod sealing cones, base O-ring, head gasket at least.
Then, depending on mileage and what you'll find during dismantling, a new set of rings, and maybe new connecting rod bearings..
If I was you, I'll put new valves and new valves guides because these break without any warning ruining the motor.