"I suggest to renovate the museum so that people could enjoy a learning process." There are a couple of things to look at in this sentence. 1. "I suggest to renovate..." This should be stated in one of the following ways: "I suggest renovating..." "I suggest the renovation of..." "I suggest (whomever is responsible) renovate..." 2. "...so that people could enjoy a learning process." "...so that people can enjoy THE learning process." Using 'the' instead of 'a' is preferred here because you are speaking of a specific learning process - that of the museum's exhibits. The use of 'could' means only a possibility. The use of 'can' means a more definite outcome. I could cross the street. (It is potentially possible as an option.) I can cross the street. (I am completely capable of doing so.) The difference between the two is subtle, but it is noticeable. Does that make sense?

First, we need to say, I suggest that the museum be renovated. We would say can instead of could, if we are talking about the present/ future. If we're talking about the past, we'd say, I suggested that the museum be renovated so that people could... Hope that helps! Steve

You can have both. "could" indicates that the situation is hypothetical. Sometimes the same situation can be considered as both really possible (can) and still hypothetical (could). In other cases, it is clear that it is either real or hypothetical.