Can I adjust the temperature of the water in my radiators?
Boilers typically have a aquastat, high limit, low limit in one of several configurations.

This is an all in one unit specific to oil. 
 
www.inspectopedia.com

Most aquastats look something like this on the outside 


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If you have conventional radiators high limit set to 150 max is common, convectors you can go to 180. It's usually best to run as low temp as possible but with oil it's very important to maintain a minimum chimney(stack) temperature. Low return temperatures can cause acid in the chimney. Now baseboard rads are split between the two types.

This is a conventional and beautiful cast iron radiator 

www.allaboutrads.co.uk

This is the inside of a fin tube convector 

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If your baseboard rads are copper tube fin type like the convector image, you can go up to 180. If they are cast iron you should keep the temperature lower because the surface gets very hot to the touch. 

If you have any pictures of the controls attached to the system they would be helpful. Just keep in mind, oil is finicky and needs yearly service by a reputable technician.